# terminator
[![logo](https://avatars1.githubusercontent.com/u/31987273?v=4&s=110)][async-url]

inform an iterable when it is prematurely terminated by the consumer. 

[![NPM version][npm-image]][npm-url]
[![Travis Status][travis-image]][travis-url]
[![Travis Status][codecov-image]][codecov-url]

### Install
```
yarn add @async-generators/terminator
```

This package's `main` entry points to a `commonjs` dist. 
The `module` entry points to a `es2015` module dist. Both require require native async-generator support, or be down-compiled with a webpack loader. 

## Api

### terminator(source)

<code>terminator()</code> returns an iterable that, when iterated, wraps the source iterable and captures calls to `return`. When a compliant consumer (`for`, `for-await`) terminates iteration, then the `return` call is rerouted to call `next(Symbol.for("terminated"))`. The original `source` iterable can then find out if it was terminated by examining the return value of `yield` to see if it equals `Symbol.for("terminated")`;

source must have a `[Symbol.asyncIterator]` or `[Symbol.iterator]` property. If both are present only `[Symbol.asyncIterator]` is used. 

## Example

example.js
```js
const terminator = require("@async-generators/terminator").default;

async function* source() {
  for (let i = 0; i < 10; i++) {
    let terminated = (yield i) == Symbol.for("terminated");
    if (terminated) {
      console.log("clean-up on aisle five!");
      return;
    }
  }
}

async function main(){
  for await (let item of terminator(source())){
    if(item > 4){
      break;
    }
    console.log(item);
  }
}

main().catch(console.log);
```

Execute with the latest node.js: 

```
node --harmony-async-iteration example.js
```

output:
```
0
1
2
3
4
clean-up on aisle five!
```
## Typescript

This library is fully typed and can be imported using: 

```ts
import terminator from '@async-generators/terminator');
```

It is also possible to directly execute your [properly configured](https://stackoverflow.com/a/43694282/1657476) typescript with [ts-node](https://www.npmjs.com/package/ts-node):

```
ts-node --harmony_async_iteration example.ts
```

[npm-url]: https://npmjs.org/package/@async-generators/terminator
[npm-image]: https://img.shields.io/npm/v/@async-generators/terminator.svg
[npm-downloads]: https://img.shields.io/npm/dm/@async-generators/terminator.svg
[travis-url]: https://travis-ci.org/async-generators/terminator
[travis-image]: https://img.shields.io/travis/async-generators/terminator/master.svg
[codecov-url]: https://codecov.io/gh/async-generators/terminator
[codecov-image]: https://codecov.io/gh/async-generators/terminator/branch/master/graph/badge.svg
[async-url]: https://github.com/async-generators