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The read-only blocking property of the HTMLScriptElement returns a live DOMTokenList object containing the operations that should be blocked on the fetching of an external resource. It reflects the <script> element's blocking content attribute.
A live 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 value property. You can also modify the DOMTokenList object using the add(), remove(), replace(), and toggle() methods.
<script id="el" async blocking="render"></script>
const el = document.getElementById("el");
console.log(el.blocking); // Output: DOMTokenList ["render"]
| Specification |
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| HTML # dom-script-blocking |
This page was last modified on Aug 16, 2026 by MDN contributors.
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