stack-base-iterator

Base class for iterators whose values come from a stack of asynchronous functions.

npm install stack-base-iterator

Subclass StackBaseIterator and push functions that call their value callback with an IteratorResult. The base class provides async iteration, next(), forEach(), and lifecycle methods.

var StackBaseIterator = require('stack-base-iterator').default;

class YourIterator extends StackBaseIterator {
  constructor(values) {
    super();
    values.forEach(function (value) {
      this.push(function (_iterator, callback) {
        callback(null, { done: false, value: value });
      });
    }, this);
  }
}

The subclass above is illustrative. A real subclass would push functions that perform its asynchronous work.

Consume values

Use async iteration when the runtime supports it:

var iterator = new YourIterator([1, 2, 3]);

(async function () {
  try {
    for await (var value of iterator) {
      console.log(value);
    }
  } finally {
    iterator.destroy();
  }
})();

For callback processing, call forEach(fn, { callbacks: true, concurrency: 1 }, done). Without callbacks: true, fn may return a value or promise. Set concurrency to control parallel processing. Call next() to retrieve one IteratorResult at a time, and destroy() to stop the iterator.