# How can I shuffle an array? [duplicate]

Use the modern version of the Fisherâ€“Yates shuffle algorithm:

``````/**
* Shuffles array in place.
* @param {Array} a items An array containing the items.
*/
function shuffle(a) {
var j, x, i;
for (i = a.length - 1; i > 0; i--) {
j = Math.floor(Math.random() * (i + 1));
x = a[i];
a[i] = a[j];
a[j] = x;
}
return a;
}
``````

## ES2015 (ES6) version

``````/**
* Shuffles array in place. ES6 version
* @param {Array} a items An array containing the items.
*/
function shuffle(a) {
for (let i = a.length - 1; i > 0; i--) {
const j = Math.floor(Math.random() * (i + 1));
[a[i], a[j]] = [a[j], a[i]];
}
return a;
}
``````

Note however, that swapping variables with destructuring assignment causes significant performance loss, as of October 2017.

## Use

``````var myArray = ['1','2','3','4','5','6','7','8','9'];
shuffle(myArray);
``````

## Implementing prototype

Using `Object.defineProperty` (method taken from this SO answer) we can also implement this function as a prototype method for arrays, without having it show up in loops such as `for (i in arr)`. The following will allow you to call `arr.shuffle()` to shuffle the array `arr`:

``````Object.defineProperty(Array.prototype, 'shuffle', {
value: function() {
for (let i = this.length - 1; i > 0; i--) {
const j = Math.floor(Math.random() * (i + 1));
[this[i], this[j]] = [this[j], this[i]];
}
return this;
}
});
``````