Fastest way to convert JavaScript NodeList to Array? – Dev

The best answers to the question “Fastest way to convert JavaScript NodeList to Array?” in the category Dev.

QUESTION:

Previously answered questions here said that this was the fastest way:

//nl is a NodeList
var arr = Array.prototype.slice.call(nl);

In benchmarking on my browser I have found that it is more than 3 times slower than this:

var arr = [];
for(var i = 0, n; n = nl[i]; ++i) arr.push(n);

They both produce the same output, but I find it hard to believe that my second version is the fastest possible way, especially since people have said otherwise here.

Is this a quirk in my browser (Chromium 6)? Or is there a faster way?

EDIT: For anyone who cares, I settled on the following (which seems to be the fastest in every browser that I tested):

//nl is a NodeList
var l = []; // Will hold the array of Node's
for(var i = 0, ll = nl.length; i != ll; l.push(nl[i++]));

EDIT2: I found an even faster way

// nl is the nodelist
var arr = [];
for(var i = nl.length; i--; arr.unshift(nl[i]));

ANSWER:

2021 update: nodeList.forEach() is now standard and supported in all current browsers (around 95% on both dekstop & mobile).

So you can simply do:

document.querySelectorAll('img').forEach(highlight);

Other cases

If you for some reason want to convert it to an array, not just iterate over it – which is a completely relevant use-case – you can use [...destructuring] or Array.from since ES6

let array1 = [...mySetOfElements];
// or
let array2 = Array.from(mySetOfElements);

This also works for other array-like structures that aren’t NodeLists

  • HTMLCollection returned by e.g. document.getElementsByTagName
  • objects with a length property and indexed elements
  • iterable objects (objects such as Map and Set)



Outdated 2010 Answer

The second one tends to be faster in some browsers, but the main point is that you have to use it because the first one is just not cross-browser. Even though The Times They Are a-Changin’

@kangax (IE 9 preview)

Array.prototype.slice can now convert
certain host objects (e.g. NodeList’s)
to arrays — something that majority of
modern browsers have been able to do
for quite a while.

Example:

Array.prototype.slice.call(document.childNodes);

ANSWER:

With ES6, we now have a simple way to create an Array from a NodeList: the Array.from() function.

// nl is a NodeList
let myArray = Array.from(nl)

ANSWER:

In ES6 you can either use:

  • Array.from

    let array = Array.from(nodelist)

  • Spread operator

    let array = [...nodelist]

ANSWER:

Here’s a new cool way to do it using the ES6 spread operator:

let arr = [...nl];