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queue-microtask
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The queue-microtask npm package provides a way to queue tasks to run after the current JavaScript event loop tick, but before rendering or IO. This is useful for deferring less critical work until after more important tasks have completed without causing significant delays.
Deferring execution
This feature allows you to defer the execution of a function until after the current event loop tick has completed, but before the browser's rendering process begins. It's useful for optimizing performance by ensuring that critical tasks are not delayed by less critical ones.
queueMicrotask(() => {
console.log('This runs after the current event loop tick but before rendering.');
});
queueMicrotask
shim for modern enginesqueueMicrotask
in all modern JS engines.queueMicrotask
in modern environments (optimal performance)Promise.resolve().then(fn)
in Node.js 10 and earlier, and old browsers (optimal performance)npm install queue-microtask
const queueMicrotask = require('queue-microtask')
queueMicrotask(() => { /* this will run soon */ })
queueMicrotask
and why would one use it?The queueMicrotask
function is a WHATWG standard. It queues a microtask to be executed prior to control returning to the event loop.
A 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 event loop.
The code queueMicrotask(fn)
is equivalent to the code Promise.resolve().then(fn)
. It is also very similar to process.nextTick(fn)
in Node.
Using microtasks lets code run without interfering with any other, potentially higher priority, code that is pending, but before the JS engine regains control over the execution context.
See the spec or Node documentation for more information.
This package allows you to use queueMicrotask
safely in all modern JS engines. Use it if you prioritize small JS bundle size over support for old browsers.
process.nextTick
?In Node, queueMicrotask
and process.nextTick
are essentially equivalent, though there are subtle differences that don't matter in most situations.
If you just need to support Node 12 and later, use queueMicrotask
directly. If you need to support all versions of Node, use this package.
setTimeout(fn, 0)
?This approach is the most compatible, but it has problems. Modern browsers throttle timers severely, so setTimeout(…, 0)
usually takes at least 4ms to run. Furthermore, the throttling gets even worse if the page is backgrounded. If you have many setTimeout
calls, then this can severely limit the performance of your program.
immediate
or asap
?These packages are great! However, if you prioritize small JS bundle size over optimal performance in old browsers then you may want to consider this package.
This package (queue-microtask
) is four times smaller than immediate
, twice as small as asap
, and twice as small as using process.nextTick
and letting the browser bundler shim it automatically.
Note: This package throws an exception in JS environments which lack Promise
support -- which are usually very old browsers and Node.js versions.
Since the queueMicrotask
API is supported in Node.js, Chrome, Firefox, Safari, Opera, and Edge, the vast majority of users will get optimal performance. Any JS environment with Promise
, which is almost all of them, also get optimal performance. If you need support for JS environments which lack Promise
support, use one of the alternative packages.
In computer programming, a shim is a library that transparently intercepts API calls and changes the arguments passed, handles the operation itself or redirects the operation elsewhere. – Wikipedia
This package could also be described as a "ponyfill".
A ponyfill is almost the same as a polyfill, but not quite. Instead of patching functionality for older browsers, a ponyfill provides that functionality as a standalone module you can use. – PonyFoo
queueMicrotask(fn)
The queueMicrotask()
method queues a microtask.
The fn
argument is a function to be executed after all pending tasks have completed but before yielding control to the browser's event loop.
MIT. Copyright (c) Feross Aboukhadijeh.
FAQs
fast, tiny `queueMicrotask` shim for modern engines
The npm package queue-microtask receives a total of 29,978,027 weekly downloads. As such, queue-microtask popularity was classified as popular.
We found that queue-microtask demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 1 open source maintainer collaborating on the project.
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