# p-each-series [](https://travis-ci.com/github/sindresorhus/p-each-series)
> Iterate over promises serially
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.
## Install
```
$ npm install p-each-series
```
## Usage
```js
const pEachSeries = require('p-each-series');
const keywords = [
getTopKeyword(), //=> Promise
'rainbow',
'pony'
];
const iterator = async element => saveToDiskPromise(element);
(async () => {
console.log(await pEachSeries(keywords, iterator));
//=> ['unicorn', 'rainbow', 'pony']
})();
```
## API
### pEachSeries(input, iterator)
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`.
#### input
Type: `Iterable<Promise | unknown>`
Iterated over serially in the `iterator` function.
#### iterator(element, index)
Type: `Function`
Return value is ignored unless it's `Promise`, then it's awaited before continuing with the next iteration.
### pEachSeries.stop
Stop iterating through items by returning `pEachSeries.stop` from the iterator function.
```js
const pEachSeries = require('p-each-series');
// Logs `a` and `b`.
const result = await pEachSeries(['a', 'b', 'c'], value => {
console.log(value);
if (value === 'b') {
return pEachSeries.stop;
}
});
console.log(result);
//=> ['a', 'b', 'c']
```
## Related
- [p-map-series](https://github.com/sindresorhus/p-map-series) - Map over promises serially
- [p-series](https://github.com/sindresorhus/p-series) - Run promise-returning & async functions in series
- [p-pipe](https://github.com/sindresorhus/p-pipe) - Compose promise-returning & async functions into a reusable pipeline
- [p-waterfall](https://github.com/sindresorhus/p-waterfall) - Run promise-returning & async functions in series, each passing its result to the next
- [p-reduce](https://github.com/sindresorhus/p-reduce) - Reduce a list of values using promises into a promise for a value
- [p-map](https://github.com/sindresorhus/p-map) - Map over promises concurrently
- [More…](https://github.com/sindresorhus/promise-fun)
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