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javascriptarraysnodelist

Fastest way to convert JavaScript NodeList to Array?

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?

Solution

  • 2021 update: nodeList.forEach() is now standard and supported in all current browsers (around 95% on both desktop & 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    Outdated 2010 Answer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);