---
title: Arrays
description:
image:
tags: js
lintConfig:
MD004:
style: "consistent"
MD006: false
published: false
---
# Creating Arrays
## `Array.from()`
The `Array.from()` static method creates a new, shallow-copied `Array` instance from an array-like or iterable object.

Array.from('hello'));    // Array [ "h", "e", "l", "l", "o" ]
Array.from([1, 2, 3, 4], x => x ** x))    // Array [1, 4, 27, 256]

`Array.from()` lets you create Arrays from:
* array-like objects (objects with a `length` property and indexed elements)
* iterable objects (objects such as `Map` and `Set`).
## `Array.isArray()`
The Array.isArray() method determines whether the passed value is an Array.

### `instanceof` vs `isArray`
When checking for Array instance, `Array.isArray` is preferred over `instanceof` because it works through iframes.

const iframe = document.createElement('iframe');
document.body.appendChild(iframe);
xArray = window.frames[window.frames.length-1].Array;
const arr = new xArray(1,2,3); // [1,2,3]

// Correctly checking for Array
Array.isArray(arr);  // true
// Considered harmful, because doesn't work through iframes
arr instanceof Array; // false

## `Array.of()`
The Array.of() method creates a new Array instance from a variable number of arguments, regardless of number or type of the arguments.

The difference between Array.of() and the Array constructor is in the handling of integer arguments: Array.of(7) creates an array with a single element, 7, whereas Array(7) creates an empty array with a length property of 7. (That implies an array of 7 empty slots, not slots with actual undefined values.)