kaczor6418/JavaScript-find-filter-map-reduce

My own implementation of filter, find, map and reduce methods

find, filter, map, reduece

My own javaScript implementation of those functions

Prerequisites

To use functions you need only web browser, but if you want to run test you need node.js and karma

Google Chrome, node.js, karma, karma-cli

Short about functions

.find

• it is a method which task is find element from array that fits our conditions
• .find returns first value that will find in this array
• if array does not contain any element that fits conditions, .find will return undefined
• .find does not modify the original array
• .find accepts callBack function as parameter which adopts 1 parameter :
  • cur -> current element of array

const numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9];
const evenNumber = numbers.find( number => number % 2 === 0 );
console.log(evenNumber); // 2

My implementation

.filter

• It is a method which task is filtering arrays
• .filter returns array with elements that fits filtering rules
• if array does not contain any element that fits conditions, .filter will return empty array
• .filter does not modify the original array
• .filter accepts callBack function as parameter which adopts 3 parameters :
  • cur -> current element of array
  • idx -> index of current element
  • src -> parent element of current element

const numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9];
const evenNumbers = numbers.filter( number => number % 2 === 0 );
console.log(evenNumbers); // (4) [2, 4, 6, 8]

My implementation

.map

• It is a method which task is modify arrays
• .map returns array of modified elements
• if array does not contain any element that fits conditions, .map will return undefined
• .map does not modify the original array
• .map accepts callBack function as parameter which adopts 3 parameters :
  • cur -> current element of array
  • idx -> index of current element
  • src -> parent element of current element

const numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9];
const onlyEvenNumbers = numbers.map( number => number * 2);
console.log(onlyEvenNumbers); // (9) [2, 4, 6, 8, 10, 12, 14, 16, 18]

My implementation

.reduce

• It is a method which task is reducing arrays
• .reduce returns structure(array, object, sting, list, set ...) of reduced elements
• if array does not contain any element that should be reduced, .reduce will return undefined
• .reduce does not modify the original array
• .reduce accepts callBack function as parameter which adopts 4 parameters and initialization structure :
  • acc -> accumulator of whole previous elements saved in initial structure
  • cur -> current element of array
  • idx -> index of current element
  • src -> parent element of current element
• if we don't send the init structure then this init value will be equals constructor of the first element of array

const numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9];
const sumOfNumbers = numbers.reduce( (acc, cur) => {
    return acc + cur;
});
console.log(sumOfNumbers); // 45

My implementation

Built With

• Vanilla JavaScript - the programming language of HTML and the Web
• Node.js - is an open source server environment
• Jasmine - JavaScript unit testing framework

Authors

• Krzysztof Kaczyński - Independent work - kaczor6418

License

This project is licensed under the MIT License - see the LICENSE.md file for details