/JavaScript-Coding-Practice

Some JavaScript Coding Practice Questions with their solutions.

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JavaScript Coding Practice

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Q. Write a function to accept argument like sum(num1)(num2); or sum(num1,num2);

Example 1:

Input: sum(10)(20);
Output: 30
Explanation: 10 + 20 = 30

Example 2:

Input: sum(10, 20);
Output: 30
Explanation: 10 + 20 = 30
Answer 
function sum(x, y) {
  if (y !== undefined) {
    return x + y;
  } else {
    return function (y) {
      return x + y;
    };
  }
}

console.log(sum(10, 20));
console.log(sum(10)(20));

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Q. Write a function to get the difference between two arrays?

Example:

Input:
var a1 = ['a', 'b'];
var a2 = ['a', 'b', 'c', 'd'];

Output:
["c", "d"]
Answer 
let arr1 = ['a', 'b'];
let arr2 = ['a', 'b', 'c', 'd'];

let difference = arr2.filter(x => !arr1.includes(x));

Q. Write a function to accept argument like [array1].diff([array2]);

Example:

Input: [1, 2, 3, 4, 5, 6].diff([3, 4, 5]);
Output: [1, 2, 6];
Answer 
Array.prototype.diff = function (a) {
  return this.filter(function (i) {
    return a.indexOf(i) < 0;
  });
};

const dif1 = [1, 2, 3, 4, 5, 6].diff([3, 4, 5]);
console.log(dif1); // => [1, 2, 6]

Q. Validate file size and extension before file upload in JavaScript?

Answer 
<!DOCTYPE html>
<html>
<head>
  <title>JavaScript File Upload Example</title>
  <script type="text/javascript">
    function showFileSize() {
      var input, file, extension;

      input = document.getElementById("fileinput");
      file = input.files[0];
      extension = file.name.substring(file.name.lastIndexOf(".") + 1);

      console.log("File Name: " + file.name);
      console.log("File Size: " + file.size + " bytes");
      console.log("File Extension: " + extension);
    }
  </script>
</head>

<body>
  <form action="#" onsubmit="return false;">
    <input type="file" id="fileinput" />
    <input type="button" id="btnLoad" value="Load" onclick="showFileSize();" />
  </form>
</body>
</html>

<!-- Output -->

File Name: pic.jpg 
File Size: 1159168 bytes 
File Extension: jpg

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Q. Create a captcha using javascript?

Answer 
<!DOCTYPE html>
<html>
  <head>
    <title>JavaScript Captcha Example</title>
  </head>
  <script>
    var captcha;

    function generateCaptcha() {
      captcha = Math.floor(Math.random() * 1000000);
      document.getElementById("captcha").value = captcha;
    }
  </script>

  <body onload="generateCaptcha()">
    <input type="text" id="captcha" disabled /><br /><br />
    <button onclick="generateCaptcha()">Refresh</button>
  </body>
</html>

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Q. Create a stopwatch in javascript?

Answer 
<!DOCTYPE html>
<html>
  <head>
    <title>Stopwatch Example</title>
  </head>

  <body>
    <h4>Time: <span id="time">00:00:00</span><h4> <br /><br />
    <button id="start" onclick="start()">Start</button>
    <button id="stop" onclick="stop()">Stop</button>
    <button id="reset" onclick="reset()">Reset</button>

    <script type="text/javascript">
      const time = document.getElementById("time");
      const startBtn = document.getElementById("start");

      let timer;
      let seconds = 0;
      let hours = 0;
      let minutes = 0;
      let MINUTES_IN_HOUR = 60;
      let SECONDS_IN_MINUTE = 60;

      function updateTimer() {
        seconds++;
        if (seconds >= SECONDS_IN_MINUTE) {
          seconds = 0;
          minutes++;
          if (minutes >= MINUTES_IN_HOUR) {
            minutes = 0;
            hours++;
          }
        }

        time.textContent =
          (hours ? (hours > 9 ? hours : "0" + hours) : "00") +
          ":" +
          (minutes ? (minutes > 9 ? minutes : "0" + minutes) : "00") +
          ":" +
          (seconds > 9 ? seconds : "0" + seconds);

        // start timer again
        start();
      }

      function start() {
        timer = setTimeout(updateTimer, 1000);
        startBtn.disabled = true;
      }

      function stop() {
        clearTimeout(timer);
        startBtn.disabled = false;
      }

      function reset() {
        time.textContent = "00:00:00";
        seconds = 0;
        minutes = 0;
        hours = 0;
        startBtn.disabled = false;
      }

      window.start = start;
      window.reset = reset;
      window.stop = stop;
    </script>
  </body>
</html>

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Q. Write a program to reverse a string?

Answer 
function reverseString(str) {
  let stringRev = "";
  for (let i = str.length; i >= 0; i--) {
    stringRev = stringRev + str.charAt(i);
  }
  return stringRev;
}
console.log(reverseString("Hello"));

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Q. Create a Promise to accept car names as argument and send response once the argument matches with Maruti?

Answer 
async function myCars(name) {
  const promise = new Promise((resolve, reject) => {
    name === "Maruti" ? resolve(name) : reject(name);
  });

  const result = await promise;
  console.log(result); // "resolved!"
}

myCars("Maruti");

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Q. Write a function to merge two JavaScript Object dynamically?

Example:

Input:

const person = {
  name: "Tanvi",
  age: 28
};

const address = {
  addressLine1: "Some Location x",
  addressLine2: "Some Location y",
  city: "Bangalore"
};

Output:

// Now person should have 5 properties 
name, age, addressLine1, addressLine2, city
Answer

Write merge function which will take two object and add all the own property of second object into first object.

Method 1: Using ES6, Object.assign method:

const merge = (toObj, fromObj) => Object.assign(toObj, fromObj);

console.log(merge(person, address));
// {name: "Tanvi", age: 28, addressLine1: "Some Location x", addressLine2: "Some Location y", city: "Bangalore"}

Method 2: Without using built-in function:

function mergeObject(toObj, fromObj) {
  // Make sure both of the parameter is an object
  if (typeof toObj === "object" && typeof fromObj === "object") {
    for (var pro in fromObj) {
      // Assign only own properties not inherited properties
      if (fromObj.hasOwnProperty(pro)) {
        toObj[pro] = fromObj[pro];
      }
    }
  } else {
    throw "Merge function can apply only on object";
  }
}

console.log(mergeObject(person, address));
// {name: "Tanvi", age: 28, addressLine1: "Some Location x", addressLine2: "Some Location y", city: "Bangalore"}

⚝ Try this example on CodeSandbox

Q. Being told that an unsorted array contains (n - 1) of n consecutive numbers (where the bounds are defined), find the missing number in O(n) time?

Example:

Input:
array = [2, 5, 1, 4, 9, 6, 3, 7];
upperBound = 9;
lowerBound = 1;

Output:
8
Answer 
/**
 *  Find theoretical sum of the consecutive numbers using a variation of Gauss Sum.
 *  Formula: [(Max * (Max + 1)) / 2] - [(Min * (Min - 1)) / 2];
 *  Max is the upper bound and Min is the lower bound
 */
function findMissingNumber(arrayOfIntegers, upperBound, lowerBound) {
  
  var sumOfIntegers = 0;
  for (var i = 0; i < arrayOfIntegers.length; i++) {
    sumOfIntegers += arrayOfIntegers[i];
  }

  upperLimitSum = (upperBound * (upperBound + 1)) / 2;
  lowerLimitSum = (lowerBound * (lowerBound - 1)) / 2;

  theoreticalSum = upperLimitSum - lowerLimitSum;

  return theoreticalSum - sumOfIntegers;
}

Q. Write a function to remove duplicates from an array in JavaScript?

Answer

1. Using set():

const names = ['John', 'Paul', 'George', 'Ringo', 'John'];

let unique = [...new Set(names)];
console.log(unique); // 'John', 'Paul', 'George', 'Ringo'

2. Using filter():

const names = ['John', 'Paul', 'George', 'Ringo', 'John'];

let x = (names) => names.filter((v,i) => names.indexOf(v) === i)
x(names); // 'John', 'Paul', 'George', 'Ringo'

3. Using forEach():

const names = ['John', 'Paul', 'George', 'Ringo', 'John'];

function removeDups(names) {
  let unique = {};
  names.forEach(function(i) {
    if(!unique[i]) {
      unique[i] = true;
    }
  });
  return Object.keys(unique);
}

removeDups(names); // // 'John', 'Paul', 'George', 'Ringo'

Q. Given a string, reverse each word in the sentence

Example:

Input: "Hello World";
Output: "olleH dlroW";
Answer 
const str = "Hello World";

let reverseEntireSentence = reverseBySeparator(str, "");

console.log(reverseBySeparator(reverseEntireSentence, " "));

function reverseBySeparator(string, separator) {
  return string.split(separator).reverse().join(separator);
}

Q. Implement enqueue and dequeue using only two stacks

Enqueue means to add an element, dequeue to remove an element.

Answer 
var inputStack = []; // First stack
var outputStack = []; // Second stack

// For enqueue, just push the item into the first stack
function enqueue(stackInput, item) {
  return stackInput.push(item);
}

function dequeue(stackInput, stackOutput) {
  // Reverse the stack such that the first element of the output stack is the
  // last element of the input stack. After that, pop the top of the output to
  // get the first element that was ever pushed into the input stack
  if (stackOutput.length <= 0) {
    while(stackInput.length > 0) {
      var elementToOutput = stackInput.pop();
      stackOutput.push(elementToOutput);
    }
  }

  return stackOutput.pop();
}

Q. Use a closure to create a private counter?

Example:

You can create a function within an outer function (a closure) that allows you to update a private variable but the variable wouldn't be accessible from outside the function without the use of a helper function.

Answer 
function counter() {
  var _counter = 0;
  // return an object with several functions that allow you
  // to modify the private _counter variable
  return {
    add: function (increment) {
      _counter += increment;
    },
    retrieve: function () {
      return "The counter is currently at: " + _counter;
    },
  };
}

// error if we try to access the private variable like below
// _counter;

// usage of our counter function
var c = counter();
c.add(5);
c.add(9);

// now we can access the private variable in the following way
c.retrieve(); // => The counter is currently at: 14

Q. Write a function to divide an array into multiple equal parts?

Example:

Input: [10, 20, 30, 40, 50];
Length: 3
Output: 
[10, 20, 30]
[40, 50]
Answer 
const arr = [10, 20, 30, 40, 50];
let lenth = 3;

function split(len) {
  while (arr.length > 0) {
    console.log(arr.splice(0, len));
  }
}
split(lenth);

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Q. Write a random integers function to print integers with in a range?

Example:

Input: 1, 100
Output: 63
Answer 
/**
 * function to return a random number 
 * between min and max range
 */
function randomInteger(min, max) {
  return Math.floor(Math.random() * (max - min + 1) ) + min;
}

randomInteger(1, 100); // returns a random integer from 1 to 100

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Q. Write a function to convert decimal number to binary number?

Example 01:

Input: 10
Output: 1010

Example 02:

Input: 7
Output: 111
Answer 
function DecimalToBinary(number) {
  let bin = 0;
  let rem,
    i = 1;
  while (number !== 0) {
    rem = number % 2;
    number = parseInt(number / 2);
    bin = bin + rem * i;
    i = i * 10;
  }
  console.log(`Binary: ${bin}`);
}

DecimalToBinary(10);

Example 02: Convert Decimal to Binary Using toString()

let val = 10;

console.log(val.toString(2)); // 1010  ==> Binary Conversion
console.log(val.toString(8)); // 12  ==> Octal Conversion
console.log(val.toString(16)); // A  ==> Hexadecimal Conversion

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Q. Write a function make first letter of the string in an uppercase?

Example:

Input: hello world
Output: Hello World
Answer

You can create a function which uses chain of string methods such as charAt, toUpperCase and slice methods to generate a string with first letter in uppercase.

function capitalizeFirstLetter(string) {
  let arr = string.split(" ");
  for (var i = 0; i < arr.length; i++) {
    arr[i] = arr[i].charAt(0).toUpperCase() + arr[i].slice(1);
  }
  return arr.join(" ");
}

console.log(capitalizeFirstLetter("hello world")); // Hello World

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Q. Write a function which will test string as a literal and as an object?

Example 01:

Input:  const ltrlStr = "Hi I am string literal";
Output: It is a string literal

Example 02:

Input:  const objStr = new String("Hi I am string object");
Output: It is an object of string
Answer

The typeof operator can be use to test string literal and instanceof operator to test String object.

function check(str) {
  if (str instanceof String) {
    return "It is an object of string";
  } else {
    if (typeof str === "string") {
      return "It is a string literal";
    } else {
      return "another type";
    }
  }
}

var ltrlStr = "Hi I am string literal";
var objStr = new String("Hi I am string object");

console.log(check(ltrlStr)); // It is a string literal
console.log(check(objStr)); // It is an object of string

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Q. How do you reversing an array?

Answer

You can use reverse() method is used reverse the elements in an array. This method is useful to sort an array in descending order. Let us see the usage of reverse() method in an example,

const fruits = ["Apple", "Banana", "Mango", "Orange"];

const reversed = fruits.reverse();
console.log('reversed:', reversed);
// expected output: "reversed:" Array ["Orange", "Mango", "Banana", "Apple"]

Q. How do you find min and max value in an array?

Example:

Input: [50, 20, 70, 60, 45, 30];
Output:
Min: 20
Max: 70
Answer

You can use Math.min and Math.max methods on array variable to find the minimum and maximum elements with in an array. Let us create two functions to find the min and max value with in an array,

var marks = [50, 20, 70, 60, 45, 30];

function findMin(arr) {
  return Math.min.apply(null, arr);
}
function findMax(arr) {
  return Math.max.apply(null, arr);
}

console.log(findMin(marks));
console.log(findMax(marks));

Q. How do you find min and max values without Math functions?

Answer

You can write functions which loops through an array comparing each value with the lowest value or highest value to find the min and max values. Let us create those functions to find min an max values,

var marks = [50, 20, 70, 60, 45, 30];

function findMin(arr) {
  var length = arr.length;
  var min = Infinity;
  while (length--) {
    if (arr[length] < min) {
      min = arr[length];
    }
  }
  return min;
}

function findMax(arr) {
  var length = arr.length;
  var max = -Infinity;
  while (length--) {
    if (arr[length] > max) {
      max = arr[length];
    }
  }
  return max;
}

console.log(findMin(marks));
console.log(findMax(marks));

Q. Check if object is empty or not using javaScript?

Answer 
function isEmpty(obj) {
  return Object.keys(obj).length === 0;
}

const obj = {};
console.log(isEmpty(obj));

⚝ Try this example on CodeSandbox

Q. Write a function to validate an email using regular expression?

Answer 
function validateEmail(email) {
  const re = /\S+@\S+\.\S+/;
  return re.test(email);
}

console.log(validateEmail("pradeep.vwa@gmail.com")); // true

⚝ Try this example on CodeSandbox

Q. Use RegEx to test password strength in JavaScript?

Answer 
let newPassword = "Pq5*@a{J";
const regularExpression = new RegExp(
  "^(?=.*[a-z])(?=.*[A-Z])(?=.*[0-9])(?=.*[!@#$%^&*])(?=.{8,})"
);

if (!regularExpression.test(newPassword)) {
  alert("Password should contain atleast one number and one special character !");
} else {
  console.log("PASS");
}

// Output
PASS
RegEx Description
^ The password string will start this way
(?=.*[a-z]) The string must contain at least 1 lowercase alphabetical character
(?=.*[A-Z]) The string must contain at least 1 uppercase alphabetical character
(?=.*[0-9]) The string must contain at least 1 numeric character
(?=.[!@#$%^&]) The string must contain at least one special character, but we are escaping reserved RegEx characters to avoid conflict
(?=.{8,}) The string must be eight characters or longer

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Q. Write a script that returns the number of occurrences of character given a string as input

Answer 
function countCharacters(str) {
  return str.replace(/ /g, "").toLowerCase().split("").reduce((p, c) => {
      if (c in p) {
        p[c]++;
      } else {
        p[c] = 1;
      }
      return p;
    }, {});
}
console.log(countCharacters("the brown fox jumps over the lazy dog"));

Q. Write a function that return the number of occurrences of a character in paragraph?

Answer 
function charCount(str, searchChar) {
  let count = 0;
  if (str) {
    let stripStr = str.replace(/ /g, "").toLowerCase(); //remove spaces and covert to lowercase
    for (let chr of stripStr) {
      if (chr === searchChar) {
        count++;
      }
    }
  }
  return count;
}
console.log(charCount("the brown fox jumps over the lazy dog", "o"));

Q. Write a recursive and non-recursive Factorial function?

Answer 
function recursiveFactorial(n) {
  if (n < 1) {
    throw Error("Value of N has to be greater then 1");
  }
  if (n === 1) {
    return 1;
  } else {
    return n * recursiveFactorial(n - 1);
  }
}

console.log(recursiveFactorial(5));

function factorial(n) {
  if (n < 1) {
    throw Error("Value of N has to be greater then 1");
  }
  if (n === 1) {
    return 1;
  }
  let result = 1;
  for (let i = 1; i <= n; i++) {
    result = result * i;
  }
  return result;
}

console.log(factorial(5));

Q. Write a recursive and non recursive fibonacci-sequence?

Answer 
// 1, 1, 2, 3, 5, 8, 13, 21, 34

function recursiveFibonacci(num) {
  if (num <= 1) {
    return 1;
  } else {
    return recursiveFibonacci(num - 1) + recursiveFibonacci(num - 2);
  }
}

console.log(recursiveFibonacci(8));

function fibonnaci(num) {
  let a = 1,
    b = 0,
    temp;
  while (num >= 0) {
    temp = a;
    a = a + b;
    b = temp;
    num--;
  }
  return b;
}

console.log(fibonnaci(7));

// Memoization fibonnaci

function fibonnaci(num, memo = {}) {
  if (num in memo) {
    return memo[num];
  }
  if (num <= 1) {
    return 1;
  }
  return (memo[num] = fibonnaci(num - 1, memo) + fibonnaci(num - 2, memo));
}

console.log(fibonnaci(5)); // 8

Q. Generate a random Number between min and max?

Answer 
// 5 to 7
let min = 5;
let max = 7;
console.log(min + Math.floor(Math.random() * (max - min + 1)));

Q. Write a function to reverse the number?

Answer 
function reverse(num) {
  let result = 0;
  while (num != 0) {
    result = result * 10;
    result = result + (num % 10);
    num = Math.floor(num / 10);
  }
  return result;
}

console.log(reverse(12345));

Q. How to perform deep copy of object or clone of object?

Answer 
function deepExtend(out = {}) {
  for (let i = 1; i < arguments.length; i++) {
    let obj = arguments[i];
    if (obj == null)
      // skip undefined and null [check with double equal not triple]
      continue;

    obj = Object(obj);

    for (let key in obj) {
      // avoid shadow hasownproperty of parent
      if (Object.prototype.hasOwnProperty.call(obj, key)) {
        if (
          typeof obj[key] === "object" &&
          !Array.isArray(obj[key]) &&
          obj[key] != null
        )
          out[key] = deepExtend(out[key], obj[key]);
        else out[key] = obj[key];
      }
    }
  }
  return out;
}

//Alternative if there are no function
let cloneObj = JSON.parse(JSON.stringify(obj));

console.log(deepExtend({}, { a: 1, b: { c: 2, d: 3 } }, { e: 4, b: { f: 1 } }));
//output : { a: 1, b: {c: 2, d: 3, f: 1}, e: 4 }

Q. Write a function to reverse an array?

Answer 
let a = [10, 20, 30, 40, 50];

//Approach 1:
console.log(a.reverse());

//Approach 2:
let reverse = a.reduce((prev, current) => {
  prev.unshift(current);
  return prev;
}, []);

console.log(reverse);

Q. Rotate 2D array

Example:

Input:
[1, 2, 3, 4],
[5, 6, 7, 8],
[9, 10, 11, 12]


Output:
[1, 5, 9]
[2, 6, 10]
[3, 7, 11]
[4, 8, 12]
Answer 
const transpose = (arr) => arr[0].map((col, i) => arr.map((row) => row[i]));

console.log(
  transpose([
    [1, 2, 3, 4],
    [5, 6, 7, 8],
    [9, 10, 11, 12],
  ])
);

Q. Get Column from 2D Array

Answer 
const getColumn = (arr, n) => arr.map((x) => x[n]);

const twoDimensionalArray = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9],
];

console.log(getColumn(twoDimensionalArray, 1)); //Result = [2,5,8]

Q. Get top N from array

Answer 
function topN(arr, num) {
  let sorted = arr.sort((a, b) => a - b);
  return sorted.slice(sorted.length - num, sorted.length);
}

console.log(topN([1, 8, 3, 4, 5], 2)); // [5,8]

Q. Get query params from Object

Answer 
function getQueryParams(obj) {
  let parms = "";
  for (let key in obj) {
    if (obj.hasOwnProperty(key)) {
      if (parms.length > 0) {
        parms += "&";
      }
      parms += encodeURI(`${key}=${obj[key]}`);
    }
  }
  return parms;
}

console.log(
  getQueryParams({
    name: "Umesh",
    tel: "48289",
    add: "3333 emearld st",
  })
);

Q. Consecutive 1's in binary

Answer 
function consecutiveOne(num) {
  let binaryArray = num.toString(2);

  let maxOccurence = 0,
    occurence = 0;
  for (let val of binaryArray) {
    if (val === "1") {
      occurence += 1;
      maxOccurence = Math.max(maxOccurence, occurence);
    } else {
      occurence = 0;
    }
  }
  return maxOccurence;
}
//13 = 1101 = 2
//5 = 101 = 1
console.log(consecutiveOne(5)); //1

Q. Spiral travesal of matrix

Answer 
var input = [
  [1, 2, 3, 4],
  [5, 6, 7, 8],
  [9, 10, 11, 12],
  [13, 14, 15, 16],
];

var spiralTraversal = function (matriks) {
  let result = [];
  var goAround = function (matrix) {
    if (matrix.length === 0) {
      return;
    }

    // right
    result = result.concat(matrix.shift());

    // down
    for (var j = 0; j < matrix.length - 1; j++) {
      result.push(matrix[j].pop());
    }

    // bottom
    result = result.concat(matrix.pop().reverse());

    // up
    for (var k = matrix.length - 1; k > 0; k--) {
      result.push(matrix[k].shift());
    }

    return goAround(matrix);
  };

  goAround(matriks);

  return result;
};
console.log(spiralTraversal(input)); // [1, 2, 3, 4, 8, 12, 16, 15, 14, 13, 9, 5, 6, 7, 11, 10]

Q. Merge Sorted array and sort it.

Answer 
function mergeSortedArray(arr1, arr2) {
  return [...new Set(arr1.concat(arr2))].sort((a, b) => a - b);
}

console.log(mergeSortedArray([1, 2, 3, 4, 5, 6], [0, 3, 4, 7])); // [0, 1, 2, 3, 4, 5, 6, 7]

Q. Anagram of words

Answer 
const alphabetize = (word) => word.split("").sort().join("");

function groupAnagram(wordsArr) {
  return wordsArr.reduce((p, c) => {
    const sortedWord = alphabetize(c);
    if (sortedWord in p) {
      p[sortedWord].push(c);
    } else {
      p[sortedWord] = [c];
    }
    return p;
  }, {});
}

console.log(
  groupAnagram(["map", "art", "how", "rat", "tar", "who", "pam", "shoop"])
);
// result : {
//  amp: ["map", "pam"],
//  art: ["art", "rat", "tar"],
//  hoops: ["shoop"],
//  how: ["how", "who"]
// }

Q. Print the largest (maximum) hourglass sum found in 2d array.

Answer 
// if arr 6 X 6 then iterate it till 4 X 4  [reduce by two]
// if arr 8 X 8 then iterate it till 6 X 6  [reduce by two]
function main(arr) {
  let maxScore = -999;
  let len = arr.length;
  for (let i = 0; i < len - 2; i++) {
    for (let j = 0; j < len - 2; j++) {
      let total =
        arr[i][j] +
        arr[i][j + 1] +
        arr[i][j + 2] +
        arr[i + 1][j + 1] +
        arr[i + 2][j] +
        arr[i + 2][j + 1] +
        arr[i + 2][j + 2];

      maxScore = Math.max(maxScore, total);
    }
  }
  console.log(maxScore);
}

Q. Transform array of object to array

Answer 
let data = [
  { vid: "aaa", san: 12 },
  { vid: "aaa", san: 18 },
  { vid: "aaa", san: 2 },
  { vid: "bbb", san: 33 },
  { vid: "bbb", san: 44 },
  { vid: "aaa", san: 100 },
];

let newData = data.reduce((acc, item) => {
  acc[item.vid] = acc[item.vid] || { vid: item.vid, san: [] };
  acc[item.vid]["san"].push(item.san);
  return acc;
}, {});

console.log(Object.keys(newData).map((key) => newData[key]));

// Result
// [[object Object] {
//   san: [12, 18, 2, 100],
//   vid: "aaa"
// }, [object Object] {
//   san: [33, 44],
//   vid: "bbb"
// }]

Q. Create a private variable or private method in object

Answer 
let obj = (function () {
  function getPrivateFunction() {
    console.log("this is private function");
  }
  let p = "You are accessing private variable";
  return {
    getPrivateProperty: () => {
      console.log(p);
    },
    callPrivateFunction: getPrivateFunction,
  };
})();

obj.getPrivateValue(); // You are accessing private variable
console.log("p" in obj); // false
obj.callPrivateFunction(); // this is private function

Q. Flatten only Array not objects

Answer 
function flatten(arr, result = []) {
  arr.forEach((val) => {
    if (Array.isArray(val)) {
      flatten(val, result);
    } else {
      result.push(val);
    }
  });
  return result;
}

let input = [1, { a: [2, [3]] }, 4, [5, [6]], [[7, ["hi"]], 8, 9], 10];
console.log(flatten(input)); // [1, { a: [2, [3]]}, 4, 5, 6, 7, "hi", 8, 9, 10]

function flattenIterative(out) {
  // iteratively
  let result = out;
  while (result.some(Array.isArray)) {
    result = [].concat.apply([], result);
  }
  return result;
}
var list1 = [
  [0, 1],
  [2, 3],
  [4, 5],
];
console.log(flattenIterative(list1)); // [0, 1, 2, 3, 4, 5]

function flattenIterative1(current) {
  let result = [];
  while (current.length) {
    let firstValue = current.shift();
    if (Array.isArray(firstValue)) {
      current = firstValue.concat(current);
    } else {
      result.push(firstValue);
    }
  }
  return result;
}

let input = [1, { a: [2, [3]] }, 4, [5, [6]], [[7, ["hi"]], 8, 9], 10];
console.log(flattenIterative1(input));
var list2 = [0, [1, [2, [3, [4, [5]]]]]];
console.log(flattenIterative1(list2)); // [0, 1, 2, 3, 4, 5]

Q. Find max difference between two number in Array

Answer 
function maxDifference(arr) {
  let maxDiff = 0;

  for (let i = 0; i < arr.length; i++) {
    for (let j = i + 1; j < arr.length; j++) {
      let diff = Math.abs(arr[i] - arr[j]);
      maxDiff = Math.max(maxDiff, diff);
    }
  }
  return maxDiff;
}

console.log(maxDifference([1, 2, 4])); // [1 - 4 ] = 3

Q. swap two number in ES6 [destructing]

Answer 
let a = 10, b = 5;

[a, b] = [b, a];

Q. Panagram ? it means all the 26 letters of alphabet are there

Answer 
function panagram(input) {
  if (input == null) {
    // Check for null and undefined
    return false;
  }

  if (input.length < 26) {
    // if length is less then 26 then it is not
    return false;
  }
  input = input.replace(/ /g, "").toLowerCase().split("");
  let obj = input.reduce((prev, current) => {
    if (!(current in prev)) {
      prev[current] = current;
    }
    return prev;
  }, {});
  console.log(Object.keys(obj).length === 26 ? "panagram" : "not pangram");
}
processData("We promptly judged antique ivory buckles for the next prize"); // pangram
processData("We promptly judged antique ivory buckles for the prize"); // Not Pangram

Q. Given two identical DOM trees (not the same one), and a node from one of them find the node in the other one.

Answer 
function indexOf(arrLike, target) {
  return Array.prototype.indexOf.call(arrLike, target);
}

// Given a node and a tree, extract the nodes path
function getPath(root, target) {
  var current = target;
  var path = [];
  while (current !== root) {
    let parentNode = current.parentNode;
    path.unshift(indexOf(parentNode.childNodes, current));
    current = parentNode;
  }
  return path;
}

// Given a tree and a path, let\'s locate a node
function locateNodeFromPath(node, path) {
  return path.reduce((root, index) => root.childNodes[index], node);
}

const rootA = document.querySelector("#root-a");
const rootB = document.querySelector("#root-b");
const target = rootA.querySelector(".person__age");

console.log(locateNodeFromPath(rootB, getPath(rootA, target)));

Q. Convert a number into a Roman Numeral

Answer 
function romanize(num) {
  let lookup = {
      M: 1000,
      CM: 900,
      D: 500,
      CD: 400,
      C: 100,
      XC: 90,
      L: 50,
      XL: 40,
      X: 10,
      IX: 9,
      V: 5,
      IV: 4,
      I: 1,
    },
    roman = "";
  for (let i in lookup) {
    while (num >= lookup[i]) {
      roman += i;
      num -= lookup[i];
    }
  }
  return roman;
}

console.log(romanize(3)); // III

Q. check if parenthesis is malformed or not

Answer 
function matchParenthesis(str) {
  let obj = { "{": "}", "(": ")", "[": "]" };
  let result = [];
  for (let s of str) {
    if (s === "{" || s === "(" || s === "[") {
      // All opening brackets
      result.push(s);
    } else {
      if (result.length > 0) {
        let lastValue = result.pop(); //pop the last value and compare with key
        if (obj[lastValue] !== s) {
          // if it is not same then it is not formated properly
          return false;
        }
      } else {
        return false; // empty array, there is nothing to pop. so it is not formated properly
      }
    }
  }
  return result.length === 0;
}

console.log(matchParenthesis("}{{}}"), matchParenthesis("{{[]}}")); // false - true

Q. Create Custom Event Emitter class

Answer 
class EventEmitter {
  constructor() {
    this.holder = {};
  }

  on(eventName, fn) {
    if (eventName && typeof fn === "function") {
      this.holder[eventName] = this.holder[eventName] || [];
      this.holder[eventName].push(fn);
    }
  }

  emit(eventName, ...args) {
    let eventColl = this.holder[eventName];
    if (eventColl) {
      eventColl.forEach((callback) => callback(args));
    }
  }
}

let e = new EventEmitter();
e.on("callme", function (args) {
  console.log(`you called me ${args}`);
});
e.on("callme", function (args) {
  console.log(`testing`);
});

e.emit("callme", ["a", "b"], { firstName: "umesh", lastName: "gohil" });

Q. Move all zero's to end

Answer 
const moveZeroToEnd = (arr) => {
  for (let i = 0, j = 0; j < arr.length; j++) {
    if (arr[j] !== 0) {
      if (i < j) {
        [arr[i], arr[j]] = [arr[j], arr[i]]; // swap i and j
      }
      i++;
    }
  }
  return arr;
};

console.log(moveZeroToEnd([1, 8, 2, 0, 0, 0, 3, 4, 0, 5, 0])); // [1, 8, 2, 3, 4, 5, 0, 0, 0, 0, 0]

Q. Decode message in matrix [diagional down right, diagional up right]

Answer 
const decodeMessage = (mat) => {
  // check if matrix is null or empty
  if (mat == null || mat.length === 0) {
    return "";
  }
  let x = mat.length - 1;
  let y = mat[0].length - 1;
  let message = "";
  let decode = (mat, i = 0, j = 0, direction = "DOWN") => {
    message += mat[i][j];

    if (i === x) {
      direction = "UP";
    }

    if (direction === "DOWN") {
      i++;
    } else {
      i--;
    }

    if (j === y) {
      return;
    }

    j++;
    decode(mat, i, j, direction);
  };
  decode(mat);
  return message;
};

let mat = [
  ["I", "B", "C", "A", "L", "K", "A"],
  ["D", "R", "F", "C", "A", "E", "A"],
  ["G", "H", "O", "E", "L", "A", "D"],
  ["G", "H", "O", "E", "L", "A", "D"],
];

console.log(decodeMessage(mat)); //IROELEA

Q. find a pair in array, whose sum is equal to given number?

Answer 
const hasPairSum = (arr, sum) => {
  if (arr == null && arr.length < 2) {
    return false;
  }

  let left = 0;
  let right = arr.length - 1;
  let result = false;

  while (left < right && !result) {
    let pairSum = arr[left] + arr[right];
    if (pairSum < sum) {
      left++;
    } else if (pairSum > sum) {
      right--;
    } else {
      result = true;
    }
  }
  return result;
};

console.log(hasPairSum([1, 2, 4, 5], 8)); // null
console.log(hasPairSum([1, 2, 4, 4], 8)); // [2,3]

const hasPairSum = (arr, sum) => {
  let difference = {};
  let hasPair = false;
  arr.forEach((item) => {
    let diff = sum - item;
    if (!difference[diff]) {
      difference[item] = true;
    } else {
      hasPair = true;
    }
  });
  return hasPair;
};
console.log(hasPairSum([6, 4, 3, 8], 8));

// NOTE: if array is not sorted then subtract the value with sum and store in difference
// then see if that value exist in difference then return true.

Q. Binary Search [Array should be sorted]

Answer 
function binarySearch(arr, val) {
  let startIndex = 0,
    stopIndex = arr.length - 1,
    middleIndex = Math.floor((startIndex + stopIndex) / 2);

  while (arr[middleIndex] !== val && startIndex < stopIndex) {
    if (val < arr[middleIndex]) {
      stopIndex = middleIndex - 1;
    } else if (val > arr[middleIndex]) {
      startIndex = middleIndex + 1;
    }
    middleIndex = Math.floor((startIndex + stopIndex) / 2);
  }

  return arr[middleIndex] === val ? middleIndex : -1;
}

console.log(binarySearch([-1, 10, 22, 35, 48, 56, 67], 22));
console.log(binarySearch([-1, 10, 22, 35, 48, 56, 67], 27));

Q. Write a function to generate Pascal triangle?

Answer 
function pascalTriangle(n) {
  let last = [1],
    triangle = [last];
  for (let i = 0; i < n; i++) {
    const ls = [0].concat(last), //[0,1]           // [0,1,1]
      rs = last.concat([0]); //[1,0]           // [1,1,0]
    last = rs.map((r, i) => ls[i] + r); //[1, 1]          // [1,2,1]
    triangle = triangle.concat([last]); // [[1], [1,1]]   // [1], [1, 1], [1, 2, 1]
  }
  return triangle;
}

console.log(pascalTriangle(2));

Q. Remove array element based on object property?

Answer 
var myArray = [
  { field: "id", operator: "eq" },
  { field: "cStatus", operator: "eq" },
  { field: "money", operator: "eq" },
];

myArray = myArray.filter(function (obj) {
  return obj.field !== "money";
});

Console.log(myArray);

Output

myArray = [
    {field: "id", operator: "eq"}
    {field: "cStatus", operator: "eq"}
]

Q. Write a program to get the value of an object from a specific path?

Example:

Input:

const data = {
    user: {
        username: 'Navin Chauhan',
        password: 'Secret'
    },
    rapot: {
        title: 'Storage usage raport',
        goal: 'Remove unused data.'
    }
};

Output:
console.log(getObjectProperty(data, 'user.username')); // Navin Chauhan
Answer 
const getObjectProperty = (object, path) => {
  const parts = path.split('.');

  for (let i = 0; i < parts.length; ++i) {
      const key = parts[i];
      object = object[key];
    }
  return object;
};

Q. Find the unique number in given array?

Example:

Input: [1, 1, 3, 2, 3]
Output: 2
Answer 
const arr = [1, 1, 3, 2, 3];
const count = {};

for (const element of arr) {
  if (count[element]) {
    count[element] += 1;
  } else {
    count[element] = 1;
  }
}

console.log(count); // {1: 2, 2: 1, 3: 2}

Q. Improve the below function?

var yourself = {
  fibonacci: function (n) {
    if (n === 0) {
      return 0;
    } else if (n === 1) {
      return 1;
    } else {
      return this.fibonacci(n - 1) + this.fibonacci(n - 2);
    }
  },
};

console.log(yourself.fibonacci(2)); // 1
console.log(yourself.fibonacci(10)); // 55
Answer 
var yourself = {
  fibonacci: function (n) {
    let arr = [0, 1];
    for (let i = 2; i < n + 1; i++) {
      arr.push(arr[i - 2] + arr[i - 1]);
    }
    return arr[n];
  },
};

Q. Predict the output of the following JS code?

const a = { msg: "Hi" };
const b = a;
b.msg = "Hello";

console.log(a, b);
Answer 
{ msg: 'Hello' } { msg: 'Hello' }

Q. Predict the output of the following JS code?

let a = [1, 2, 3];
let b = [4, 5, 6];

console.log(a + b);
Answer 
1, 2, 34, 5, 6

Q. Predict the output of the following JS code?

const arr = [10, 20, 30];
arr.push(40);  
console.log(arr)

const arr1 = [10, 20, 30];
arr1 = []; 
console.log(arr1) 

const arr2 = [10, 20, 30];
arr2[2] = 50; 
console.log(arr2)
Answer 
[10, 20, 30, 40]
Error
[10, 20, 50]

Q. Predict the output of the following JS code?

var obj = {name: "neha", getName: function() {console.log(this.name);}}

var getName = obj.getName;
var obj2 = {name: "naina", getName};
obj.getName();
obj2.getName();
Answer 
Neha
Naina

Q. Predict the output of the following JS code?

const person = {name: "neha"};
const array = [person, person, person];

array[1].name = "";
console.log(array[0].name);
Answer 
undefined

Q. Predict the output of the following JS code?

var a = 1;

function b() {
  a = 10;
  return;

  function a() {}
}

b();
console.log(a);
Answer 
1

Q. Predict the output of the following NodeJS code?

console.log('A');

setImmediate(()=>{console.log('setImmediate')});

process.nextTick(()=>{console.log('nextTick')});

setTimeout(()=>{
  console.log('setTimeout');
},0);

console.log('C');
Answer 
A
C
nextTick
setTimeout
setImmediate

Q. Predict the output of the following NodeJS code?

console.log(1);

setTimeout(() => { console.log("setTimeout")}, 0);

console.log(2);

new Promise((resolve, reject) => {
   setTimeout(() => {
     console.log("Promise");
     resolve("done")}, 0);
});

console.log(3);
Answer 
1
2
3
setTimeout
Promise

Q. Predict the output of the following JavaScript code?

async function something() {
  console.log("1");

  let promise = new Promise((resolve, reject) => {
    setTimeout(() => {
      console.log("2");
      resolve("done!");
    }, 100);
  });

  await promise;

  setTimeout(() => {
    console.log("3");
  }, 100);
  console.log("4");
}

something();
console.log("5");
Answer 
1
5
2
4
3

Q. Predict the output of the following JavaScript code?

console.log(+"Hello");

Q. Predict the output of the following JavaScript code?

var result;
for (var i = 5; i > 0; i--) {
  result = result + i;
}
console.log(result);

Q. Predict the output of the following JavaScript code?

var a = 1.2;
console.log(typeof a);

Q. Predict the output of the following JavaScript code?

var x = 10;
if (x) {
  let x = 4;
}
console.log(x);

Q. Predict the output of the following JavaScript code?

console.log(0.1 + 0.2 == 0.3);

Q. Predict the output of the following JavaScript code?

console.log(1 + -"1" + 2);

Q. Predict the output of the following JavaScript code?

(function (x) {
  return (function (y) {
    console.log(x);
  })(10);
})(20);

Q. Predict the output of the following JavaScript code?

var num = 20;
var getNumber = function () {
  console.log(num);
  var num = 10;
};
getNumber();

Q. Predict the output of the following JavaScript code?

function f1() {
  num = 10;
}
f1();
console.log("window.num: " + window.num);

Q. Predict the output of the following JavaScript code?

console.log("(null + undefined): " + (null + undefined));

Q. Predict the output of the following JavaScript code?

(function () {
  var a = (b = 3);
})();

console.log("value of a : " + a); 
console.log("value of b : " + b);

Q. Predict the output of the following JavaScript code?

var y = 1;
if (function f() {}) {
  y += typeof f;
}
console.log(y);

Q. Predict the output of the following JavaScript code?

var k = 1;
if (1) {
  eval(function foo() {});
  k += typeof foo;
}
console.log(k);

Q. Predict the output of the following JavaScript code?

var k = 1;
if (1) {
  function foo() {}
  k += typeof foo;
}
console.log(k);

Q. Predict the output of the following JavaScript code?

console.log("(-1 / 0): " + -1 / 0); 
console.log("(1 / 0): " + 1 / 0); 
console.log("(0 / 0): " + 0 / 0); 
console.log("(0 / 1): " + 0 / 1);

Q. Predict the output of the following JavaScript code?

var a = 4;
var b = "5";
var c = 6;

console.log("(a + b): " + (a + b)); 
console.log("(a - b): " + (a - b)); 
console.log("(a * b): " + a * b); 
console.log("(a / b): " + a / b); 
console.log("(a % b): " + (a % b));

Q. Predict the output of the following JavaScript code?

console.log("MAX : " + Math.max(10, 2, NaN)); 
console.log("MAX : " + Math.max());

Q. Predict the output of the following JavaScript code?

(function () {
  var a = (b = 3);
})();

console.log("a defined? " + (typeof a !== "undefined")); 
console.log("b defined? " + (typeof b !== "undefined"));

Q. Predict the output of the following JavaScript code?

var myObject = {
  foo: "bar",
  func: function () {
    var self = this;
    console.log("outer func:  this.foo = " + this.foo); 
    console.log("outer func:  self.foo = " + self.foo); 
    (function () {
      console.log("inner func:  this.foo = " + this.foo); 
      console.log("inner func:  self.foo = " + self.foo); 
    })();
  },
};
myObject.func();

Q. Predict the output of the following JavaScript code?

console.log(0.1 + 0.2); 
console.log(0.1 + 0.2 == 0.3);

Q. Predict the output of the following JavaScript code?

(function () {
  console.log(1);
  setTimeout(function () {
    console.log(2);
  }, 1000);
  setTimeout(function () {
    console.log(3);
  }, 0);
  console.log(4);
})();

Q. Predict the output of the following JavaScript code?

var arr1 = "john".split("");
var arr2 = arr1.reverse();
var arr3 = "jones".split("");

arr2.push(arr3);

console.log("array 1: length=" + arr1.length + " last=" + arr1.slice(-1)); 
console.log("array 2: length=" + arr2.length + " last=" + arr2.slice(-1));

Q. Predict the output of the following JavaScript code?

console.log(1 + "2" + "2"); 
console.log(1 + +"2" + "2"); 
console.log(1 + -"1" + "2"); 
console.log(+"1" + "1" + "2"); 
console.log("A" - "B" + "2"); 
console.log("A" - "B" + 2);

Q. Predict the output of the following JavaScript code?

for (var i = 0; i < 5; i++) {
  setTimeout(function () {
    console.log(i);
  }, i * 1000);
}

Q. Predict the output of the following JavaScript code?

for (var i = 0; i < 5; i++) {
  (function (x) {
    setTimeout(function () {
      console.log(x);
    }, x * 1000);
  })(i);
}
//Output:- 0, 1, 2, 3, 4

Q. Predict the output of the following JavaScript code?

console.log("0 || 1 = " + (0 || 1)); 
console.log("1 || 2 = " + (1 || 2)); 
console.log("0 && 1 = " + (0 && 1)); 
console.log("1 && 2 = " + (1 && 2));

Q. Predict the output of the following JavaScript code?

console.log(false == "0"); 
console.log(false === "0");

Q. Predict the output of the following JavaScript code?

var a = {},
  b = { key: "b" },
  c = { key: "c" };

a[b] = 123;
a[c] = 456;
console.log(a[b]);

Q. Predict the output of the following JavaScript code?

console.log(
  (function f(n) {
    return n > 1 ? n * f(n - 1) : n;
  })(10)
);

Q. Predict the output of the following JavaScript code?

(function (x) {
  return (function (y) {
    console.log(x); //1
  })(2);
})(1);

Q. Predict the output of the following JavaScript code?

var hero = {
  _name: "John Doe",
  getSecretIdentity: function () {
    return this._name;
  },
};
var stoleSecretIdentity = hero.getSecretIdentity;

console.log(stoleSecretIdentity()); 
console.log(hero.getSecretIdentity());

Q. Predict the output of the following JavaScript code?

var length = 10;
function fn() {
  console.log(this.length);
}

var obj = {
  length: 5,
  method: function (fn) {
    fn();
    arguments[0]();
  },
};

obj.method(fn, 1);

Q. Predict the output of the following JavaScript code?

(function () {
  try {
    throw new Error();
  } catch (x) {
    var x = 1,
      y = 2;
    console.log(x);
  }
  console.log(x);
  console.log(y);
})();

Q. Predict the output of the following JavaScript code?

var x = 21;
var girl = function () {
  console.log(x); 
  var x = 20;
};
girl();

Q. Predict the output of the following JavaScript code?

console.log(1 < 2 < 3); 
console.log(3 > 2 > 1);

Q. Predict the output of the following JavaScript code?

console.log(typeof typeof 1);

Q. Predict the output of the following JavaScript code?

var b = 1;
function outer() {
  var b = 2;
  function inner() {
    b++;
    var b = 3;
    console.log(b);
  }
  inner();
}
outer();

Q. Predict the output of the following JavaScript code?

x = 10;
console.log(x);
var x;

Q. Predict the output of the following JavaScript code?

const arr = [1, 2];
arr.push(3);

Q. Predict the output of the following JavaScript code?

var o = new F();
o.constructor === F;

Q. Predict the output of the following JavaScript code?

let sum = (a, b) => {
  a + b;
};
console.log(sum(10, 20));

Q. Predict the output of the following JavaScript code?

var arr = ["javascript", "typescript", "es6"];

var searchValue = (value) => {
  return arr.filter((item) => {
    return item.indexOf(value) > -1;
  });
};

console.log(searchValue("script"));

Q. Write a program that prints the numbers from 1 to 15. But for multiples of three print “Fizz” instead of the number and for the multiples of five print “Buzz”. For numbers which are multiples of both three and five print “FizzBuzz”?

Example:

Input: 15
Output: 
1
2
Fizz
4
Buzz
Fizz
7
8
Fizz
Buzz
11
Fizz
13
14
FizzBuzz
Answer

Solution - 01:

for (var i = 1; i <= 15; i++) {
  if (i % 15 == 0) console.log("FizzBuzz");
  else if (i % 3 == 0) console.log("Fizz");
  else if (i % 5 == 0) console.log("Buzz");
  else console.log(i);
}

Solution - 02:

for (var i = 1; i <= 15; i++) {
  var f = i % 3 == 0,
    b = i % 5 == 0;
  console.log(f ? (b ? "FizzBuzz" : "Fizz") : b ? "Buzz" : i);
}

Q. What will be the output of the following code?

var output = (function (x) {
  delete x;
  return x;
})(0);

console.log(output);
Answer

The code above will output 0 as output. delete operator is used to delete a property from an object. Here x is not an object it's local variable. delete operator doesn't affect local variables.

Q. What will be the output of the following code?

var x = 1;
var output = (function () {
  delete x;
  return x;
})();

console.log(output);
Answer

The code above will output 1 as output. delete operator is used to delete a property from an object. Here x is not an object it's global variable of type number.

Q. What will be the output of the following code?

var x = { foo: 1 };
var output = (function () {
  delete x.foo;
  return x.foo;
})();

console.log(output);
Answer

The code above will output undefined as output. delete operator is used to delete a property from an object. Here x is an object which has foo as a property and from a self-invoking function, we are deleting the foo property of object x and after deletion, we are trying to reference deleted property foo which result undefined.

Q. What will be the output of the following code?

var Employee = {
  company: "xyz",
};
var emp1 = Object.create(Employee);
delete emp1.company;
console.log(emp1.company);
Answer

The code above will output xyz as output. Here emp1 object got company as prototype property. delete operator doesn't delete prototype property.

emp1 object doesn't have company as its own property. you can test it console.log(emp1.hasOwnProperty('company')); //output : false However, we can delete company property directly from Employee object using delete Employee.company or we can also delete from emp1 object using __proto__ property delete emp1.__proto__.company.

Q. What will be the output of the following code?

var trees = ["xyz", "xxxx", "test", "ryan", "apple"];
delete trees[3];
console.log(trees.length);
Answer

The code above will output 5 as output. When we used delete operator for deleting an array element then, the array length is not affected by this. This holds even if you deleted all elements of an array using delete operator.

So when delete operator removes an array element that deleted element is no longer present in the array. In place of value at deleted index undefined x 1 in chrome and undefined is placed at the index. If you do console.log(trees) output ["xyz", "xxxx", "test", undefined × 1, "apple"] in Chrome and in Firefox ["xyz", "xxxx", "test", undefined, "apple"].

Q. What will be the output of the following code?

var bar = true;
console.log(bar + 0);
console.log(bar + "xyz");
console.log(bar + true);
console.log(bar + false);
Answer

The code above will output 1, "truexyz", 2, 1 as output. Here's a general guideline for the plus operator:

  • Number + Number -> Addition
  • Boolean + Number -> Addition
  • Boolean + Boolean -> Addition
  • Number + String -> Concatenation
  • String + Boolean -> Concatenation
  • String + String -> Concatenation

Q. What will be the output of the following code?

var z = 1,
  y = (z = typeof y);
console.log(y);
Answer

The code above will print string "undefined" as output. According to associativity rule operator with the same precedence are processed based on their associativity property of operator. Here associativity of the assignment operator is Right to Left so first typeof y will evaluate first which is string "undefined" and assigned to z and then y would be assigned the value of z. The overall sequence will look like that:

var z;
z = 1;
var y;
z = typeof y;
y = z;

Q. What will be the output of the following code?

// NFE (Named Function Expression)
var foo = function bar() {
  return 12;
};
typeof bar();
Answer

The output will be Reference Error. To fix the bug we can try to rewrite the code a little bit:

Sample 1:

var bar = function () {
  return 12;
};
typeof bar();

or

Sample 2:

function bar() {
  return 12;
}
typeof bar();

The function definition can have only one reference variable as a function name, In sample 1 bar is reference variable which is pointing to anonymous function and in sample 2 we have function statement and bar is the function name.

var foo = function bar() {
  // foo is visible here
  // bar is visible here
  console.log(typeof bar()); // Works here :)
};
// foo is visible here
// bar is undefined here

Q. What is the output of the following?

bar();
(function abc() {
  console.log("something");
})();
function bar() {
  console.log("bar got called");
}
Answer

The output will be :

bar got called
something

Since the function is called first and defined during parse time the JS engine will try to find any possible parse time definitions and start the execution loop which will mean function is called first even if the definition is post another function.

Q. What will be the output of the following code?

var salary = "1000$";

(function () {
  console.log("Original salary was " + salary);

  var salary = "5000$";

  console.log("My New Salary " + salary);
})();
Answer

The code above will output: undefined, 5000$ because of hoisting. In the code presented above, you might be expecting salary to retain it values from outer scope until the point that salary was re-declared in the inner scope. But due to hoisting salary value was undefined instead. To understand it better have a look of the following code, here salary variable is hoisted and declared at the top in function scope. When we print its value using console.log the result is undefined. Afterwards the variable is redeclared and the new value "5000$" is assigned to it.

var salary = "1000$";

(function () {
  var salary = undefined;
  console.log("Original salary was " + salary);

  salary = "5000$";

  console.log("My New Salary " + salary);
})();

Q. What would be the output of the following code?

function User(name) {
  this.name = name || "JsGeeks";
}

var person = (new User("xyz")["location"] = "USA");
console.log(person);
Answer

The output of above code would be "USA". Here new User("xyz") creates a brand new object and created property location on that and USA has been assigned to object property location and that has been referenced by the person.

Let say new User("xyz") created a object called foo. The value "USA" will be assigned to foo["location"], but according to ECMAScript Specification , pt 12.14.4 the assignment will itself return the rightmost value: in our case it's "USA". Then it will be assigned to person.

To better understand What is going on here, try to execute this code in console, line by line:

function User(name) {
  this.name = name || "JS";
}

var person;
var foo = new User("xyz");
foo["location"] = "USA";
// the console will show you that the result of this is "USA"

Q. What would be the output of following code?

var strA = "hi there";
var strB = strA;
strB = "bye there!";
console.log(strA);
Answer

The output will 'hi there' because we're dealing with strings here. Strings are passed by value, that is, copied.

Q. What would be the output of following code?

var objA = { prop1: 42 };
var objB = objA;
objB.prop1 = 90;
console.log(objA);
Answer

The output will {prop1: 90} because we're dealing with objects here. Objects are passed by reference, that is, objA and objB point to the same object in memory.

Q. What would be the output of following code?

var objA = { prop1: 42 };
var objB = objA;
objB = {};
console.log(objA);
Answer

The output will {prop1: 42}.

When we assign objA to objB, the objB variable will point to the same object as the objB variable.

However, when we reassign objB to an empty object, we simply change where objB variable references to. This doesn't affect where objA variable references to.

Q. What would be the output of following code?

var arrA = [0, 1, 2, 3, 4, 5];
var arrB = arrA;
arrB[0] = 42;
console.log(arrA);
Answer

The output will be [42,1,2,3,4,5].

Arrays are object in JavaScript and they are passed and assigned by reference. This is why both arrA and arrB point to the same array [0,1,2,3,4,5]. That's why changing the first element of the arrB will also modify arrA: it's the same array in the memory.

Q. What would be the output of following code?

var arrA = [0, 1, 2, 3, 4, 5];
var arrB = arrA.slice();
arrB[0] = 42;
console.log(arrA);
Answer

The output will be [0,1,2,3,4,5].

The slice function copies all the elements of the array returning the new array. That's why arrA and arrB reference two completely different arrays.

Q. What would be the output of following code?

var arrA = [
  { prop1: "value of array A!!" },
  { someProp: "also value of array A!" },
  3,
  4,
  5,
];
var arrB = arrA;
arrB[0].prop1 = 42;
console.log(arrA);
Answer

The output will be [{prop1: 42}, {someProp: "also value of array A!"}, 3,4,5].

Arrays are object in JS, so both varaibles arrA and arrB point to the same array. Changing arrB[0] is the same as changing arrA[0]

Q. What would be the output of following code?

var arrA = [
  { prop1: "value of array A!!" },
  { someProp: "also value of array A!" },
  3,
  4,
  5,
];
var arrB = arrA.slice();
arrB[0].prop1 = 42;
arrB[3] = 20;
console.log(arrA);
Answer

The output will be [{prop1: 42}, {someProp: "also value of array A!"}, 3,4,5].

The slice function copies all the elements of the array returning the new array. However, it doesn't do deep copying. Instead it does shallow copying. You can imagine slice implemented like this:

function slice(arr) {
  var result = [];
  for (i = 0; i < arr.length; i++) {
    result.push(arr[i]);
  }
  return result;
}

Look at the line with result.push(arr[i]). If arr[i] happens to be a number or string, it will be passed by value, in other words, copied. If arr[i] is an object, it will be passed by reference.

In case of our array arr[0] is an object {prop1: "value of array A!!"}. Only the reference to this object will be copied. This effectively means that arrays arrA and arrB share first two elements.

This is why changing the property of arrB[0] in arrB will also change the arrA[0].

Q. console.log(employeeId);

Answer

ReferenceError: employeeId is not defined

Q. What would be the output of following code?

console.log(employeeId);
var employeeId = "19000";
Answer

undefined

Q. What would be the output of following code?

var employeeId = "1234abe";
(function () {
  console.log(employeeId);
  var employeeId = "122345";
})();
Answer

undefined

Q. What would be the output of following code?

var employeeId = "1234abe";
(function () {
  console.log(employeeId);
  var employeeId = "122345";
  (function () {
    var employeeId = "abc1234";
  })();
})();
Answer 
undefined

Q. What would be the output of following code?

(function () {
  console.log(typeof displayFunc);
  var displayFunc = function () {
    console.log("Hi I am inside displayFunc");
  };
})();
Answer

undefined

Q. What would be the output of following code?

var employeeId = "abc123";
function foo() {
  employeeId = "123bcd";
  return;
}
foo();
console.log(employeeId);
Answer

'123bcd'

Q. What would be the output of following code?

var employeeId = "abc123";

function foo() {
  employeeId = "123bcd";
  return;

  function employeeId() {}
}
foo();
console.log(employeeId);
Answer

'abc123'

Q. What would be the output of following code?

var employeeId = "abc123";

function foo() {
  employeeId();
  return;

  function employeeId() {
    console.log(typeof employeeId);
  }
}
foo();
Answer

'function'

Q. What would be the output of following code?

function foo() {
  employeeId();
  var product = "Car";
  return;

  function employeeId() {
    console.log(product);
  }
}
foo();
Answer
  1. undefined

Q. What would be the output of following code?

(function foo() {
  bar();

  function bar() {
    abc();
    console.log(typeof abc);
  }

  function abc() {
    console.log(typeof bar);
  }
})();
Answer

function function

Q. What would be the output of following code?

(function () {
  "use strict";

  var person = {
    name: "John",
  };
  person.salary = "10000$";
  person["country"] = "USA";

  Object.defineProperty(person, "phoneNo", {
    value: "8888888888",
    enumerable: true,
  });

  console.log(Object.keys(person));
})();
Answer

["name", "salary", "country", "phoneNo"]

Q. What would be the output of following code?

(function () {
  "use strict";

  var person = {
    name: "John",
  };
  person.salary = "10000$";
  person["country"] = "USA";

  Object.defineProperty(person, "phoneNo", {
    value: "8888888888",
    enumerable: false,
  });

  console.log(Object.keys(person));
})();
Answer

["name", "salary", "country"]

Q. What would be the output of following code?

(function () {
  var objA = {
    foo: "foo",
    bar: "bar",
  };
  var objB = {
    foo: "foo",
    bar: "bar",
  };
  console.log(objA == objB);
  console.log(objA === objB);
})();
Answer

false false

Q. What would be the output of following code?

(function () {
  var objA = new Object({ foo: "foo" });
  var objB = new Object({ foo: "foo" });
  console.log(objA == objB);
  console.log(objA === objB);
})();
Answer

false false

Q. What would be the output of following code?

(function () {
  var objA = Object.create({
    foo: "foo",
  });
  var objB = Object.create({
    foo: "foo",
  });
  console.log(objA == objB);
  console.log(objA === objB);
})();
Answer

false false

Q. What would be the output of following code?

(function () {
  var objA = Object.create({
    foo: "foo",
  });
  var objB = Object.create(objA);
  console.log(objA == objB);
  console.log(objA === objB);
})();
Answer

false false

Q. What would be the output of following code?

(function () {
  var objA = Object.create({
    foo: "foo",
  });
  var objB = Object.create(objA);
  console.log(objA.toString() == objB.toString());
  console.log(objA.toString() === objB.toString());
})();
Answer

true true

Q. What would be the output of following code?

(function () {
  var objA = Object.create({
    foo: "foo",
  });
  var objB = objA;
  console.log(objA == objB);
  console.log(objA === objB);
  console.log(objA.toString() == objB.toString());
  console.log(objA.toString() === objB.toString());
})();
Answer

true true true true

Q. What would be the output of following code?

(function () {
  var objA = Object.create({
    foo: "foo",
  });
  var objB = objA;
  objB.foo = "bar";
  console.log(objA.foo);
  console.log(objB.foo);
})();
Answer

bar bar

Q. What would be the output of following code?

(function () {
  var objA = Object.create({
    foo: "foo",
  });
  var objB = objA;
  objB.foo = "bar";

  delete objA.foo;
  console.log(objA.foo);
  console.log(objB.foo);
})();
Answer

foo foo

Q. What would be the output of following code?

(function () {
  var objA = {
    foo: "foo",
  };
  var objB = objA;
  objB.foo = "bar";

  delete objA.foo;
  console.log(objA.foo);
  console.log(objB.foo);
})();
Answer

undefined undefined

Q. What would be the output of following code?

(function () {
  var array = new Array("100");
  console.log(array);
  console.log(array.length);
})();
Answer

["100"] 1

Q. What would be the output of following code?

(function () {
  var array1 = [];
  var array2 = new Array(100);
  var array3 = new Array(["1", 2, "3", 4, 5.6]);
  console.log(array1);
  console.log(array2);
  console.log(array3);
  console.log(array3.length);
})();
Answer

[] [] [Array[5]] 1

Q. What would be the output of following code?

(function () {
  var array = new Array("a", "b", "c", "d", "e");
  array[10] = "f";
  delete array[10];
  console.log(array.length);
})();
Answer

11

Q. What would be the output of following code?

(function () {
  var animal = ["cow", "horse"];
  animal.push("cat");
  animal.push("dog", "rat", "goat");
  console.log(animal.length);
})();
Answer

6

Q. What would be the output of following code?

(function () {
  var animal = ["cow", "horse"];
  animal.push("cat");
  animal.unshift("dog", "rat", "goat");
  console.log(animal);
})();
Answer

[ 'dog', 'rat', 'goat', 'cow', 'horse', 'cat' ]

Q. What would be the output of following code?

(function () {
  var array = [1, 2, 3, 4, 5];
  console.log(array.indexOf(2));
  console.log([{ name: "John" }, { name: "John" }].indexOf({ name: "John" }));
  console.log([[1], [2], [3], [4]].indexOf([3]));
  console.log("abcdefgh".indexOf("e"));
})();
Answer
  1. 1 -1 -1 4

Q. What would be the output of following code?

(function () {
  var array = [1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 6];
  console.log(array.indexOf(2));
  console.log(array.indexOf(2, 3));
  console.log(array.indexOf(2, 10));
})();
Answer

1 6 -1

Q. What would be the output of following code?

(function () {
  var numbers = [2, 3, 4, 8, 9, 11, 13, 12, 16];
  var even = numbers.filter(function (element, index) {
    return element % 2 === 0;
  });
  console.log(even);

  var containsDivisibleby3 = numbers.some(function (element, index) {
    return element % 3 === 0;
  });

  console.log(containsDivisibleby3);
})();
Answer

[ 2, 4, 8, 12, 16 ] true

Q. What would be the output of following code?

(function () {
  var containers = [2, 0, false, "", "12", true];
  var containers = containers.filter(Boolean);
  console.log(containers);
  var containers = containers.filter(Number);
  console.log(containers);
  var containers = containers.filter(String);
  console.log(containers);
  var containers = containers.filter(Object);
  console.log(containers);
})();
Answer

[ 2, '12', true ] [ 2, '12', true ] [ 2, '12', true ] [ 2, '12', true ]

Q. What would be the output of following code?

(function () {
  var list = ["foo", "bar", "john", "ritz"];
  console.log(list.slice(1));
  console.log(list.slice(1, 3));
  console.log(list.slice());
  console.log(list.slice(2, 2));
  console.log(list);
})();
Answer

[ 'bar', 'john', 'ritz' ] [ 'bar', 'john' ] [ 'foo', 'bar', 'john', 'ritz' ] [] [ 'foo', 'bar', 'john', 'ritz' ]

Q. What would be the output of following code?

(function () {
  var list = ["foo", "bar", "john"];
  console.log(list.splice(1));
  console.log(list.splice(1, 2));
  console.log(list);
})();
Answer

[ 'bar', 'john' ] [] [ 'foo' ]

Q. What would be the output of following code?

(function () {
  var arrayNumb = [2, 8, 15, 16, 23, 42];
  arrayNumb.sort();
  console.log(arrayNumb);
})();
Answer

[ 15, 16, 2, 23, 42, 8 ]

Q. What would be the output of following code?

function funcA() {
  console.log("funcA ", this);
  (function innerFuncA1() {
    console.log("innerFunc1", this);
    (function innerFunA11() {
      console.log("innerFunA11", this);
    })();
  })();
}

console.log(funcA());
Answer

funcA
innerFunc1 innerFunA11

Q. What would be the output of following code?

var obj = {
  message: "Hello",
  innerMessage: !(function () {
    console.log(this.message);
  })(),
};

console.log(obj.innerMessage);
Answer

undefined true

Q. What would be the output of following code?

var obj = {
  message: "Hello",
  innerMessage: function () {
    return this.message;
  },
};

console.log(obj.innerMessage());
Answer

Hello

Q. What would be the output of following code?

var obj = {
  message: "Hello",
  innerMessage: function () {
    (function () {
      console.log(this.message);
    })();
  },
};
console.log(obj.innerMessage());
Answer

undefined

Q. What would be the output of following code?