# 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 --save p-each-series
```

## Usage

```js
const pEachSeries = require('p-each-series');

const keywords = [
	getTopKeyword() //=> Promise
	'rainbow',
	'pony'
];

const iterator = el => saveToDiskPromise(el); //=> Promise

pEachSeries(keywords, iterator).then(result => {
	console.log(result);
	//=> ['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|any>`

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.

## Related

* [p-map-series](https://github.com/sindresorhus/p-map-series) - Map over promises serially
* [p-pipe](https://github.com/sindresorhus/p-pipe) - Compose promise-returning & async functions into a reusable pipeline
* [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)

## License

MIT © [Sindre Sorhus](https://sindresorhus.com)