files/en-us/web/api/htmlscriptelement/blocking/index.md
{{APIRef("HTML DOM")}}
The read-only blocking property of the {{domxref("HTMLScriptElement")}} returns a live {{domxref("DOMTokenList")}} object containing the operations that should be blocked on the fetching of an external resource. It reflects the {{HTMLElement("script")}} element's blocking content attribute.
A live {{domxref("DOMTokenList")}} object.
Although the blocking property itself is read-only in the sense that you can't replace the DOMTokenList object, you can still assign to the blocking 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.
<script id="el" async blocking="render"></script>
const el = document.getElementById("el");
console.log(el.blocking); // Output: "render"
{{Specifications}}
{{Compat}}