wiki/content/20201009090331-javascript_array_methods.md

date	id	title
2020-10-09	c76b3766-a1ed-43f9-bdb6-4076e6bb5b7a	JavaScript Array Methods

ES6

Static Array methods

Array.from()

const arr2 = Array.from(arguments); // ES6

If a value is iterable (as all Array-like DOM data structure are by now), you can also use the spread operator (…) to convert it to an Array:

const arr1 = [...'abc'];
    // ['a', 'b', 'c']
const arr2 = [...new Set().add('a').add('b')];
    // ['a', 'b']

Array.of()

This returns an array of the passed parameters

console.log(Array.of(1, 2, 3, 4)) // [1, 2, 3, 4]

Array.prototype methods

Array.prototype.fill()

const arr2 = new Array(2).fill(undefined);
    // [undefined, undefined]

Array.prototype.copyWithin()

The method signature is:

Array.prototype.copyWithin(target : number,
    start : number, end = this.length) : This

It copies the elements whose indices are in the range [start,end) to index target and subsequent indices. If the two index ranges overlap, care is taken that all source elements are copied before they are overwritten. I am confused as to how this is in any way useful.

const arr = [0,1,2,3];
console.log(arr.copyWithin(2, 0, 2)) // [0, 1, 0, 1]

Searching for elements

1. Array.prototype.findIndex()

   console.log([6, -6, 8].findIndex(x => x < 0)) // 1
   

2. Array.prototype.find()

   console.log([6, -6, 8].find(x => x < 0)) // -6
   

Iteration

1. Array.prototype.entries()

   console.log(Array.from(['a', 'b'].entries())) // [ [ 0, 'a' ], [ 1, 'b' ] ]
   

2. Array.prototype.values()

   console.log(Array.from(['a', 'b'].values())) // ['a', 'b']
   

3. Array.prototype.keys()

   console.log(Array.from(['a', 'b'].keys())) // [0, 1]
   

ES2016

Array.prototype.includes()

Tells you if array includes a certain element:

console.log(["a", "b", "c"].includes("a")); // true
console.log(["a", "b", "c"].includes("d")); // false