HTMLScriptElement: blocking property - Web APIs | MDN
Value
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.
Examples
html
<script id="el" async blocking="render"></script>
js
const el = document.getElementById("el");
console.log(el.blocking); // Output: "render"
Specifications
| Specification |
|---|
| HTML # dom-script-blocking |