JavaScript Arrays

Objectives

By the end of this, developers should be able to:

Define an array
Store, access, and update data values in arrays
Iterate over items in an array

Preparation

Fork and clone this repository
Create a new branch, training, for your work and change into it.

Code Along: Arrays

In JavaScript to represent a list we can use an Array. Elements in an Array or items in our list are ordered. JavaScript arrays are zero-indexed: the first element of an array is at index 0, and the last element is at the index equal to the value of the array's length property minus 1. Using an invalid index number returns undefined.

// Create an empty array literal
const list = [];

// Create an array literal with values
const anotherList = ['Nelly', 100, false, 2];

// Read value from an Array, use index
anotherList[0]; // 'Nelly'
anotherList[2]; // false

// Update value in an Array, use index
anotherList[2] = true;
anotherList; // ['Nelly', 100, true, 2]

// Add value to an Array, use index
anotherList[5] = 'Add Me';
anotherList; // ['Nelly', 100, true, 2, undefined, 'Add Me']

Array Methods

Iterating through Arrays

Code Along: Iterate through an Array

const developers = ['Ahmad', 'Mike', 'Sami']

// Individually print message for each item in array
console.log('Hello ' + developers[0])
console.log('Hello ' + developers[1])
console.log('Hello ' + developers[2])

// Loop through array using i as the index
for (let i = 0; i < developers.length; i++) {
  console.log('Hello ' + developers[i])
}

Array Practice

Createa file named practice.js to save your solutions.

Using push and unshift, make this array contain the numbers from zero through seven:

const arr = [2, 3, 4];

// your code here

arr; // => [0, 1, 2, 3, 4, 5, 6, 7]

What is returned by push? Before throwing this into the console, form a hypothesis about what you think the return value will be:

const arr = [5, 7, 9];
arr.push(6); // returns ???

Change all odd numbers to be those numbers multiplied by two:

const numbers = [4, 9, 7, 2, 1, 8];

  // your code here

numbers; // => [8, 18, 14, 4, 2, 16]

Change all odd numbers to be those numbers multiplied by two:

const numbers = [4, 9, 7, 2, 1, 8];

  // your code here

numbers; // => [4, 18, 14, 2, 2, 8]

Create an array to hold your favorite colors. For each choice, log to the screen a string like: My #1 choice is blue.
Create an array of ages. Loop through and log only the ages that are over 21.

MicFin/week_01-day_04-js-arrays