The keys() method of the DOMTokenList interface returns an iterator allowing to go through all keys contained in this object. The keys are of type unsigned integer.





Return value

Returns an iterator.


In the following example we retrieve the list of classes set on a <span> element as a DOMTokenList using Element.classList. We when retrieve an iterator containing the keys using values(), then iterate through those keys using a for ... of loop, writing each one to the <span>'s Node.textContent.

First, the HTML:

<span class="a b c"></span>

Now the JavaScript:

var span = document.querySelector("span");
var classes = span.classList;
var iterator = classes.keys();

for(var value of iterator) {
  span.textContent += value + ' ++ ';

The output looks like this:


Specification Status Comment
The definition of 'keys() (as iterable<Node>)' in that specification.
Living Standard Initial definition

Browser compatibility

Update compatibility data on GitHub
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
keysChrome Full support 42Edge Full support 16Firefox Full support 50IE No support NoOpera Full support 32Safari Full support 10.1WebView Android Full support 45Chrome Android Full support 45Firefox Android Full support 50Opera Android Full support 32Safari iOS Full support 10.3Samsung Internet Android Full support 5.0


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