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Arrays

Arrays are lists of items.

var anotherAmazingArray = ["Three","Bs","in","a","bucket"];

 

Get, Add and Remove elements from an array

 

Array.indexOf()

 

Array.find()

 Array.find() method get the first element that satisfies a condition.

const array = [1,2,3,4,5]

let c = array.find( x => x % 2 === 0 )

// 2

 

Array.filter()

Array.filter gets all the elements that satisfy a condition

 

const array = [1,2,3,4,5]

let d = array.filter( x => x%2 === 0 )

// [2,4]

 

Array.slice()

 Array.slice gets a subset of the array from start index to the end index ( end not included )

const array = [1,2,3,4,5]

let foo = array.slice(1,4)

// [2,3,4]

 

Array.splice(startIndex, deleteCount,  ... items_to_add)

 

let letters = [ 1,2,3,4,5]

letters.splice(1,0, 6,9)

// letters : [1,6, 9,3,4,5]

 

Array.push() <- push an element to the end of the array

 

 

Array.pop() <- takes the last element

 

Array.shift() <- takes the first element

 

Array.concat() <- makes a new array

 

Array.map()

 

Array.forEach()

// Using forEach()

let arr2 = 11, 2, 31;

arr2. forEach((e) => {
  console.log(e * 2);
}) ;

//Does not return anything
// Output: 2 4 6

 

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Sort an Array

 Out of the box it does an alphabetical sort.

To numeric sort - then use a function.

let array = ['c', 'e', 'a', 't'];

//sort the array 

array.sort(); 
console. log(array);

// Output: ['a', 'c', 'e', 't']


//reverse the array 

array.reverse();
console.log(array);

// Output: ['t', 'e', 'c', 'a']

 

Reverse an Array

 

 

Array destructuring

const fruits = ['apple', 'pear', 'bannana' ]

const [a,b,c] = fruits

// a is 'apple'
// b is 'pear'
// c is 'bannana'

 

How to convert an array-like object into an array

 

var arrayLike = {0: 'a', 1: 'b', 2: 'c', length: 3}

var foo = Array.from(arrayLike)

This just takes the values from the key-value pairs.

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var foo = [...arrayLike]


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foo = {0:'aaa', 1:3, length:2}     <- the length is important

var bar = Array.from(foo)

// bar is ["aaa", 3]

 

//Array.prototype.slice.call)


var arrayLike = {0:'a', 1:'b', 2:'с', length:3}

var array3 = Array.prototype.slice.call(arrayLike)

console.log(array3)

// Output: ['a','b','c']