How to simulate JavaScript yield?

Question

One of the new mechanisms available in JavaScript 1.7 is yield, useful for generators and iterators.

This is currently supported in Mozilla browsers only (that I\'m

Answer 1

I have started a little project that tries to do this with some callback trickery. Since it's impossible to create real coroutines in "standard" JavaScript, this doesn't come without a few caveats, e.g:

• it's impossible to make this follow the iterator protocol (stuff like .next() etc.),
• it's impossible to iterate through several generators at once,
• you have to watch out not to let the wrong objects leave the generator's scope (e.g. by calling yield in a timeout – since this is "plain" JavaScript, there's no syntax restriction that prevents you from doing this),
• exceptions in the generator are a little tricky,
• and last not least, it's very experimental (just started this a few days ago).

On the bright side, you have yield! :)

The Fibonacci example from the MDC page would look like this:

var fibonacci = Generator(function () {
  var fn1 = 1;
  var fn2 = 1;
  while (1){
    var current = fn2;
    fn2 = fn1;
    fn1 = fn1 + current;
    this.yield(current);
  }
});

console.log(fibonacci.take(10).toArray());

Output:

[1, 1, 2, 3, 5, 8, 13, 21, 34, 55]

The project is on BitBucket at https://bitbucket.org/balpha/lyfe.