| 1 | # p-limit [](https://travis-ci.org/sindresorhus/p-limit)
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| 2 |
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| 3 | > Run multiple promise-returning & async functions with limited concurrency
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| 4 |
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| 5 | ## Install
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| 6 |
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| 7 | ```
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| 8 | $ npm install p-limit
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| 9 | ```
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| 10 |
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| 11 | ## Usage
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| 12 |
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| 13 | ```js
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| 14 | const pLimit = require('p-limit');
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| 15 |
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| 16 | const limit = pLimit(1);
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| 17 |
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| 18 | const input = [
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| 19 | limit(() => fetchSomething('foo')),
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| 20 | limit(() => fetchSomething('bar')),
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| 21 | limit(() => doSomething())
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| 22 | ];
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| 23 |
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| 24 | (async () => {
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| 25 | // Only one promise is run at once
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| 26 | const result = await Promise.all(input);
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| 27 | console.log(result);
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| 28 | })();
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| 29 | ```
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| 30 |
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| 31 | ## API
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| 32 |
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| 33 | ### pLimit(concurrency)
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| 34 |
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| 35 | Returns a `limit` function.
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| 36 |
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| 37 | #### concurrency
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| 38 |
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| 39 | Type: `number`\
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| 40 | Minimum: `1`\
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| 41 | Default: `Infinity`
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| 42 |
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| 43 | Concurrency limit.
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| 44 |
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| 45 | ### limit(fn, ...args)
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| 46 |
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| 47 | Returns the promise returned by calling `fn(...args)`.
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| 48 |
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| 49 | #### fn
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| 50 |
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| 51 | Type: `Function`
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| 52 |
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| 53 | Promise-returning/async function.
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| 54 |
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| 55 | #### args
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| 56 |
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| 57 | Any arguments to pass through to `fn`.
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| 58 |
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| 59 | 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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| 60 |
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| 61 | ### limit.activeCount
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| 62 |
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| 63 | The number of promises that are currently running.
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| 64 |
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| 65 | ### limit.pendingCount
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| 66 |
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| 67 | The number of promises that are waiting to run (i.e. their internal `fn` was not called yet).
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| 68 |
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| 69 | ### limit.clearQueue()
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| 70 |
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| 71 | Discard pending promises that are waiting to run.
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| 72 |
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| 73 | 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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| 74 |
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| 75 | Note: This does not cancel promises that are already running.
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| 76 |
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| 77 | ## FAQ
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| 78 |
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| 79 | ### How is this different from the [`p-queue`](https://github.com/sindresorhus/p-queue) package?
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| 80 |
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| 81 | 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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| 82 |
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| 83 | ## Related
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| 84 |
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| 85 | - [p-queue](https://github.com/sindresorhus/p-queue) - Promise queue with concurrency control
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| 86 | - [p-throttle](https://github.com/sindresorhus/p-throttle) - Throttle promise-returning & async functions
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| 87 | - [p-debounce](https://github.com/sindresorhus/p-debounce) - Debounce promise-returning & async functions
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| 88 | - [p-all](https://github.com/sindresorhus/p-all) - Run promise-returning & async functions concurrently with optional limited concurrency
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| 89 | - [More…](https://github.com/sindresorhus/promise-fun)
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| 90 |
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| 91 | ---
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| 92 |
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| 93 | <div align="center">
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| 94 | <b>
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| 95 | <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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| 96 | </b>
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| 97 | <br>
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| 98 | <sub>
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| 99 | 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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| 100 | </sub>
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| 101 | </div>
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