28 lines
803 B
Markdown
28 lines
803 B
Markdown
---
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title: pipeAsyncFunctions
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tags: function,promise,intermediate
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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()` with the spread operator (`...`) to perform left-to-right function composition using `Promise.then()`.
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The functions can return a combination of: simple values, `Promise`'s, or they can be defined as `async` ones returning through `await`.
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All functions must be unary.
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```js
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const pipeAsyncFunctions = (...fns) => 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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