23 lines
686 B
Markdown
23 lines
686 B
Markdown
---
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title: promisify
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tags: function,promise,intermediate
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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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- *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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