31 lines
883 B
Markdown
31 lines
883 B
Markdown
---
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title: Pipe async functions
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tags: function,promise
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cover: new-york-skyline
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firstSeen: 2018-01-27T18:17:44+02:00
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lastUpdated: 2020-10-22T20:24:04+03:00
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---
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Performs left-to-right function composition for asynchronous functions.
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- Use `Array.prototype.reduce()` and the spread operator (`...`) to perform function composition using `Promise.prototype.then()`.
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- The functions can return a combination of normal values, `Promise`s or be `async`, returning through `await`.
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- All functions must accept a single argument.
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```js
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const pipeAsyncFunctions = (...fns) =>
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arg => fns.reduce((p, f) => p.then(f), Promise.resolve(arg));
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```
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```js
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const sum = pipeAsyncFunctions(
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x => x + 1,
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x => new Promise(resolve => setTimeout(() => resolve(x + 2), 1000)),
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x => x + 3,
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async x => (await x) + 4
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);
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(async() => {
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console.log(await sum(5)); // 15 (after one second)
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})();
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```
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