Override the next method of an asynchronous iterator doesn't work in v10

[celicoo]

Bug Report

Current Behavior
Override the next method of an asynchronous iterator object doesn't work in v10.

Input Code

const customIterator = {
  [Symbol.asyncIterator]() {
    return {
      next: this.next
    }
  },

  next() {
    console.log('outter')
    this.next = () => {
      console.log('inner')
      return new Promise((resolve, reject) => {
        setTimeout(() => {
          resolve({
            done: false,
            value: {}
          })
        }, 1000)
      })
    }
    return this.next()
  }
}

async function test() {
  for await (const x of customIterator) {}
}
test()

Expected behavior/code
The output should be outter printed, followed by multiple inner, but in fact, the looping always prints outter and then inner, repeatedly.

Expected:

outter
inner
inner
inner
inner
...

Reality:

outter
inner
outter
inner
outter
inner

Environment

• Node/npm version: 10.3/ 5
• OS: 10.13.4

[celicoo]

I realized that Chrome and Firefox have the same behaviour of Node 10. Does that mean that the wrong behaviour happens on Node 8? (behind --harmony_async_iteration), and more important - Is it a internal cache of await for...of?

[mscdex]

Any features like that that are only available behind a flag should be considered experimental. My guess is that what you're experiencing now is the expected behavior.

[celicoo]

I'm affraid that's the case, which makes me extremely disappointed since method overriding is something that should be possible in this case.

The only way to achieve the same result that I can think of is managing state with a control variable.

[CertainPerformance]

See this StackOverflow question - it doesn't look to be a bug in Node. The same behavior is visible in native browser-based JS as well.

[bnoordhuis]

Answered, closing. Next time, please post to nodejs/help if you're not sure it's a bug in Node.js.