How to set an attribute in JavaScript?

To set an attribute in JavaScript, do this: element.setAttribute('some-attribute', 'some-value').

For example, if this is your element:

<div id="my-element">text</div>

And you set an attribute like so:

document.getElementById('my-element').setAttribute('class', 'marked');

The result will be:

<div id="my-element" class="marked">text</div>