66 lines
1.7 KiB
Markdown
66 lines
1.7 KiB
Markdown
# p-each-series [](https://travis-ci.org/sindresorhus/p-each-series)
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> Iterate over promises serially
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Useful as a side-effect iterator. Prefer [`p-map`](https://github.com/sindresorhus/p-map) if you don't need side-effects, as it's concurrent.
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## Install
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```
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$ npm install --save p-each-series
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```
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## Usage
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```js
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const pEachSeries = require('p-each-series');
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const keywords = [
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getTopKeyword() //=> Promise
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'rainbow',
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'pony'
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];
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const iterator = el => saveToDiskPromise(el); //=> Promise
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pEachSeries(keywords, iterator).then(result => {
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console.log(result);
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//=> ['unicorn', 'rainbow', 'pony']
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});
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```
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## API
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### pEachSeries(input, iterator)
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Returns a `Promise` that is fulfilled when all promises in `input` and ones returned from `iterator` are fulfilled, or rejects if any of the promises reject. The fulfillment value is the original `input`.
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#### input
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Type: `Iterable<Promise|any>`
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Iterated over serially in the `iterator` function.
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#### iterator(element, index)
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Type: `Function`
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Return value is ignored unless it's `Promise`, then it's awaited before continuing with the next iteration.
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## Related
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- [p-map-series](https://github.com/sindresorhus/p-map-series) - Map over promises serially
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- [p-pipe](https://github.com/sindresorhus/p-pipe) - Compose promise-returning & async functions into a reusable pipeline
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- [p-reduce](https://github.com/sindresorhus/p-reduce) - Reduce a list of values using promises into a promise for a value
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- [p-map](https://github.com/sindresorhus/p-map) - Map over promises concurrently
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- [More…](https://github.com/sindresorhus/promise-fun)
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## License
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MIT © [Sindre Sorhus](https://sindresorhus.com)
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