@async-generators/terminator

terminator

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

Install

yarn add @async-generators/terminator

This package's main entry points to a commonjs distribution.

Additionally, the module entry points to a es2015 distribution, which can be used by build systems, such as webpack, to directly use es2015 modules.

Api

terminator(source)

terminator() 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

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:

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

It is also possible to directly execute your properly configured typescript with ts-node:

ts-node --harmony_async_iteration example.ts