files/en-us/web/api/domtokenlist/keys/index.md
{{APIRef("DOM")}}
The keys() method of the {{domxref("DOMTokenList")}} interface
returns an {{jsxref("Iteration_protocols",'iterator',"",1)}} allowing to go through all keys contained in this object.
The keys are unsigned integers.
keys()
None.
Returns an {{jsxref("Iteration_protocols","iterator","",1)}}.
In the following example we retrieve the list of classes set on a
{{htmlelement("span")}} element as a DOMTokenList using
{{domxref("Element.classList")}}. We then retrieve an iterator containing the keys using keys(),
then iterate through those keys using a for...of loop,
writing each one to the <span>'s {{domxref("Node.textContent")}}.
First, the HTML:
<span class="a b c"></span>
Now the JavaScript:
const span = document.querySelector("span");
const classes = span.classList;
const iterator = classes.keys();
for (let value of iterator) {
span.textContent += `(${value}) `;
}
The output looks like this:
{{ EmbedLiveSample('Examples', '100%', 60) }}
{{Specifications}}
{{Compat}}