102 lines
2.7 KiB
Markdown
102 lines
2.7 KiB
Markdown
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# p-limit
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> Run multiple promise-returning & async functions with limited concurrency
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## Install
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```
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$ npm install p-limit
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```
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## Usage
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```js
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const pLimit = require('p-limit');
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const limit = pLimit(1);
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const input = [
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limit(() => fetchSomething('foo')),
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limit(() => fetchSomething('bar')),
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limit(() => doSomething())
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];
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(async () => {
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// Only one promise is run at once
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const result = await Promise.all(input);
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console.log(result);
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})();
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```
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## API
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### pLimit(concurrency)
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Returns a `limit` function.
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#### concurrency
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Type: `number`\
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Minimum: `1`\
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Default: `Infinity`
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Concurrency limit.
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### limit(fn, ...args)
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Returns the promise returned by calling `fn(...args)`.
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#### fn
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Type: `Function`
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Promise-returning/async function.
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#### args
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Any arguments to pass through to `fn`.
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Support for passing arguments on to the `fn` is provided in order to be able to avoid creating unnecessary closures. You probably don't need this optimization unless you're pushing a *lot* of functions.
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### limit.activeCount
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The number of promises that are currently running.
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### limit.pendingCount
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The number of promises that are waiting to run (i.e. their internal `fn` was not called yet).
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### limit.clearQueue()
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Discard pending promises that are waiting to run.
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This might be useful if you want to teardown the queue at the end of your program's lifecycle or discard any function calls referencing an intermediary state of your app.
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Note: This does not cancel promises that are already running.
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## FAQ
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### How is this different from the [`p-queue`](https://github.com/sindresorhus/p-queue) package?
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This package is only about limiting the number of concurrent executions, while `p-queue` is a fully featured queue implementation with lots of different options, introspection, and ability to pause the queue.
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## Related
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- [p-queue](https://github.com/sindresorhus/p-queue) - Promise queue with concurrency control
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- [p-throttle](https://github.com/sindresorhus/p-throttle) - Throttle promise-returning & async functions
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- [p-debounce](https://github.com/sindresorhus/p-debounce) - Debounce promise-returning & async functions
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- [p-all](https://github.com/sindresorhus/p-all) - Run promise-returning & async functions concurrently with optional limited concurrency
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- [More…](https://github.com/sindresorhus/promise-fun)
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---
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<div align="center">
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<b>
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<a href="https://tidelift.com/subscription/pkg/npm-p-limit?utm_source=npm-p-limit&utm_medium=referral&utm_campaign=readme">Get professional support for this package with a Tidelift subscription</a>
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</b>
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<br>
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<sub>
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Tidelift helps make open source sustainable for maintainers while giving companies<br>assurances about security, maintenance, and licensing for their dependencies.
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</sub>
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</div>
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