26 lines
766 B
Markdown
26 lines
766 B
Markdown
---
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title: Promisify function
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type: snippet
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tags: [function,promise]
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cover: duck-plants
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dateModified: 2020-10-22T20:24:04+03:00
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---
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Converts an asynchronous function to return a promise.
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- Use currying to return a function returning a `Promise` that calls the original function.
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- Use the rest operator (`...`) to pass in all the parameters.
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- **Note:** In Node 8+, you can use [`util.promisify`](https://nodejs.org/api/util.html#util_util_promisify_original).
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```js
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const promisify = func => (...args) =>
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new Promise((resolve, reject) =>
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func(...args, (err, result) => (err ? reject(err) : resolve(result)))
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);
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```
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```js
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const delay = promisify((d, cb) => setTimeout(cb, d));
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delay(2000).then(() => console.log('Hi!')); // Promise resolves after 2s
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```
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