The length read-only property of the DOMTokenList interface is an integer representing the number of objects stored in the object.
tokenList.length;
An integer.
In the following example we retrieve the list of classes set on a <span> element as a DOMTokenList using Element.classList, then write the length of the list 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 length = classes.length;
span.textContent = 'classList length = ' + length;
The output looks like this:
| Specification | Status | Comment |
|---|---|---|
| DOM The definition of 'length' in that specification. | Living Standard | Initial definition |
| Desktop | ||||||
|---|---|---|---|---|---|---|
| Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | |
| Basic support | Yes | 12 | 50 | ? | Yes | ? |
| Mobile | |||||||
|---|---|---|---|---|---|---|---|
| Android webview | Chrome for Android | Edge Mobile | Firefox for Android | Opera for Android | iOS Safari | Samsung Internet | |
| Basic support | Yes | Yes | ? | 50 | Yes | ? | Yes |
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https://developer.mozilla.org/en-US/docs/Web/API/DOMTokenList/length