break-async-iterator

break-async-iterator

Problem:

const neverResolves /*(without user input)*/ = process.stdin /* (Readable is an async iterator as of Node v10) */
async function* stuck() {
  for await (const i of neverResolves) {
    yield // never reaches
  }
}
let i = stuck()
i.next() // stuck
i.return() // still stuck

Solution

const breakAI = require('break-async-iterator')

const notStuck = breakAI(breakable => async function*() {
  try {
    for await (const i of breakable(neverResolves)) {
      yield
    }
  } finally {
    // reaches when `i.return()` or `i.throw()` is called
  }
})
let i = notStuck()
i.next() // still stuck
i.return() // but at least this can break the for-await loop

Install

npm i break-async-iterator

Usage

API

breakAI(breakable => async function* asyncGenerator(){...})

• breakable A function that takes an iterator or a promise and returns a breakable version of the same

• Returns An async generator that returns an iterator (wrapped around the one returned by asyncGenerator()) that's able to interrupt any iterators or promises (that were passed through breakable()) when its .return() or .throw() are called

Example

If you have an async generator function like this:

async function* asyncGenerator() {
  for await (const value of anotherAsyncIterator) {
    yield value
  }
  yield await aPromise
}

Then simply wrap it like this

const asyncGenerator = breakAI(breakable => async function*() {
  // and wrap any inner asyncIterators or promises with breakable:
  for await (const value of breakable(anotherAsyncIterator)) {
    yield value
  }
  yield await breakable(aPromise)
})