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86 lines
3.8 KiB
86 lines
3.8 KiB
4 years ago
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# immediate [](https://travis-ci.org/calvinmetcalf/immediate)
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[](https://ci.testling.com/calvinmetcalf/immediate)
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```
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npm install immediate --save
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```
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then
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```js
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var immediate = require("immediate");
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immediate(function () {
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// this will run soon
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});
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immediate(function (arg1, arg2) {
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// get your args like in iojs
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}, thing1, thing2);
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```
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## Introduction
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**immediate** is a microtask library, descended from [NobleJS's setImmediate](https://github.com/NobleJS/setImmediate), but including ideas from [Cujo's When](https://github.com/cujojs/when) and [RSVP][RSVP].
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immediate takes the tricks from setImmediate and RSVP and combines them with the scheduler inspired (vaguely) by when's.
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Note versions 2.6.5 and earlier were strictly speaking a 'macrotask' library not a microtask one, [see this for the difference](https://github.com/YuzuJS/setImmediate#macrotasks-and-microtasks), if you need a macrotask library, [I got you covered](https://github.com/calvinmetcalf/macrotask).
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Several new features were added in versions 3.1.0 and 3.2.0 to maintain parity with
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process.nextTick, but the 3.0.x series is still being kept up to date if you just need
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the small barebones version
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## The Tricks
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### `process.nextTick`
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Note that we check for *actual* Node.js environments, not emulated ones like those produced by browserify or similar.
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### `queueMicrotask`
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Function available in major browser these days which you can use to add a function into the microtask queue managed by V8.
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### `MutationObserver`
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This is what [RSVP][RSVP] uses, it's very fast, details on [MDN](https://developer.mozilla.org/en-US/docs/Web/API/MutationObserver).
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### `MessageChannel`
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Unfortunately, `postMessage` has completely different semantics inside web workers, and so cannot be used there. So we
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turn to [`MessageChannel`][MessageChannel], which has worse browser support, but does work inside a web worker.
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### `<script> onreadystatechange`
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For our last trick, we pull something out to make things fast in Internet Explorer versions 6 through 8: namely,
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creating a `<script>` element and firing our calls in its `onreadystatechange` event. This does execute in a future
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turn of the event loop, and is also faster than `setTimeout(…, 0)`, so hey, why not?
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## Tricks we don't use
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### `setImmediate`
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We avoid using `setImmediate` because node's `process.nextTick` is better suited to our needs. Additionally, Internet Explorer 10's implementation of `setImmediate` is broken.
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## Reference and Reading
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* [Efficient Script Yielding W3C Editor's Draft][spec]
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* [W3C mailing list post introducing the specification][list-post]
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* [IE Test Drive demo][ie-demo]
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* [Introductory blog post by Nicholas C. Zakas][ncz]
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* I wrote a couple of blog posts on this, [part 1][my-blog-1] and [part 2][my-blog-2]
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[RSVP]: https://github.com/tildeio/rsvp.js
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[spec]: https://dvcs.w3.org/hg/webperf/raw-file/tip/specs/setImmediate/Overview.html
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[list-post]: http://lists.w3.org/Archives/Public/public-web-perf/2011Jun/0100.html
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[ie-demo]: http://ie.microsoft.com/testdrive/Performance/setImmediateSorting/Default.html
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[ncz]: http://www.nczonline.net/blog/2011/09/19/script-yielding-with-setimmediate/
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[nextTick]: http://nodejs.org/docs/v0.8.16/api/process.html#process_process_nexttick_callback
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[postMessage]: http://www.whatwg.org/specs/web-apps/current-work/multipage/web-messaging.html#posting-messages
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[MessageChannel]: http://www.whatwg.org/specs/web-apps/current-work/multipage/web-messaging.html#channel-messaging
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[cross-browser-demo]: http://calvinmetcalf.github.io/setImmediate-shim-demo
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[my-blog-1]:http://calvinmetcalf.com/post/61672207151/setimmediate-etc
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[my-blog-2]:http://calvinmetcalf.com/post/61761231881/javascript-schedulers
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