files/en-us/web/api/htmloutputelement/htmlfor/index.md
{{ APIRef("HTML DOM") }}
The read-only htmlFor property of the {{domxref("HTMLOutputElement")}} returns a live {{domxref("DOMTokenList")}} object containing a list of ids of those elements contributing input values to (or otherwise affected) the calculation. It reflects the {{HTMLElement("output")}} element's for content attribute.
A live {{domxref("DOMTokenList")}} object.
Although the htmlFor property itself is read-only in the sense that you can't replace the DOMTokenList object, you can still assign to the htmlFor property directly, which is equivalent to assigning to its {{domxref("DOMTokenList/value", "value")}} property. You can also modify the DOMTokenList object using the {{domxref("DOMTokenList/add", "add()")}}, {{domxref("DOMTokenList/remove", "remove()")}}, {{domxref("DOMTokenList/replace", "replace()")}}, and {{domxref("DOMTokenList/toggle", "toggle()")}} methods.
const outputElem = document.getElementById("result");
for (const id of outputElem.htmlFor.split(" ")) {
const elem = document.getElementById(id);
elem.style.outline = "2px solid red";
}
{{Specifications}}
{{Compat}}