Purpose

Array is used to assign multiple values to a single variable

const x = ["element1", "element2"];

// empty array is also a legit array
const emptyArray = [];

// empty element is initialized as `undefined`
console.log(emptyArray[0]); // undefined

Zero-indexed

Arrays (in JS) are zero-indexed

• Meaning the element count/position starts at 0 instead of 1

const arr = [1,2,3];

// accessing first array element
arr[0]; // 1

// accessing last array element
arr[arr.length - 1]; // 3

Initialization/Creation

// basic initialization
const arr1 = [item1, item2, item3];
const arr2 = new Array('item1','item2','item3');

// Create n-length `null` values filled array
const nullArr = new Array(n).fill(null);
// fill with x number of 0s
const prefilledArr = Array(x).fill(0);

// faster initialization with `undefined` fills
const arr = []; 
arr.length = n;

Naming Conventions

Array name should be plural

Let's say there is a collection of frogs in an array

["red frog", "happy frog", "green frog"];

If we name the array as frog, then we have a list (multiple frogs) assigned to a singular variable name

• This does not accurately represent what the variable contains

/* incorrect */
// singular frog
const frog = ["red frog", "happy frog", "green frog"];

/* correct */
// multiple frogs in variable frogs
const frogs = ["red frog", "happy frog", "green frog"];

// single frog in variable frog
const frog = "happy frog";

Overriding Element

// changing value at index position 0
arr[0] = "different-element-1";

Arrays can be nested

const arrOfArr = [["iq", "ag", "bc"], ["ef", "hi"]];
arrOfArr[1] // ["ef", "hi"]
arrOfArr[1][1] // "hi"

Adding/Removing Elements

// adding element
arr.push('new_item') // adds to end of arr
arr.unshift('new_item') // adds to start of arr

// removing element
arr.pop() // removing element from the end of array
arr.shift() // removing element from the start of arrays

Iteration

// Iteration using `for` loop
const arr = [ '0', '1', '2' ];

function call_me(params) {
  for (i=0; i<params.length; i++) {
    console.log(params[i]);
  }
}

call_me(arr); // '0', '1', '2'

// Iteration using `for...of`
const wordArr = ['i', 'have', 'some', 'stings', 'inside', 'me'];

for (let value of wordArr){
  console.log(value);
}
// 'i', 'have', 'some', 'stings', 'inside', 'me'