Readable stream async iterator polyfill

readable-stream-async-iterator.js

// polyfill readable stream iterator
export const ReadableStream = window.ReadableStream && window.ReadableStream.prototype[Symbol.asyncIterator] ?
  window.ReadableStream : (() => {
  function ReadableStream (...args) {
    let readers = []
    let obj = args[0]

    let stream = new window.ReadableStream(...args)

    // patch cancel to release lock
    let _cancel = stream.cancel
    stream.cancel = function cancel(...args) {
      readers.forEach(reader => {
        reader.cancel()
        reader.releaseLock()
      })
      readers.length = 0
      _cancel.call(this, ...args)
    }

    stream[Symbol.asyncIterator] =
    stream.getIterator = function () {
      const reader = stream.getReader()
      readers.push(reader)

      return {
        next() {
          return reader.read()
        },
        return() {
          readers.splice(readers.indexOf(reader), 1)
          reader.releaseLock()
          return {}
        },
        [Symbol.asyncIterator]() {
          return this
        }
      };
    }
    return stream
  }

  return ReadableStream
})()