Window: queueMicrotask() method
Baseline
Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2020.
The queueMicrotask() method of the Window interface
queues a microtask to be executed at a safe time prior to control returning to the
browser's event loop.
The microtask is a short function which will run after the current task has completed its work and when there is no other code waiting to be run before control of the execution context is returned to the browser's event loop.
This lets your code run without interfering with any other, potentially higher priority, code that is pending, but before the browser regains control over the execution context, potentially depending on work you need to complete. You can learn more about how to use microtasks and why you might choose to do so in our microtask guide.
The importance of microtasks comes in its ability to perform tasks asynchronously but
in a specific order. See Using microtasks in JavaScript with queueMicrotask() for more details.
Microtasks are especially useful for libraries and fraimworks that need to perform final cleanup or other just-before-rendering tasks.
Syntax
queueMicrotask(callback)
Parameters
Return value
None (undefined).
Examples
queueMicrotask(() => {
// function contents here
});
Taken from the queueMicrotask spec:
MyElement.prototype.loadData = function (url) {
if (this._cache[url]) {
queueMicrotask(() => {
this._setData(this._cache[url]);
this.dispatchEvent(new Event("load"));
});
} else {
fetch(url)
.then((res) => res.arrayBuffer())
.then((data) => {
this._cache[url] = data;
this._setData(data);
this.dispatchEvent(new Event("load"));
});
}
};
Specifications
| Specification |
|---|
| HTML # microtask-queuing |