//what are generators? //they're pausable functions, pausable iterable objects, to be more precise //they're defined with the * var myGen = function*() { var one = yield 1; var two = yield 2; var three = yield 3; console.log(one, two, three); }; var gen = myGen(); //get the generator ready to run //when you run next() on a generator, it runs until a yield, then waits until next() is called again console.log(gen.next()); //{value:1, done: false} console.log(gen.next()); //{value:2, done: false} console.log(gen.next()); //{value:3, done: false} console.log(gen.next()); //{value:undefined, done: true} console.log(gen.next()); //errors because you can't call next() on a closed generator

//so yippee, when do I ever have to yield numbers? Seems silly //the magic happens when smarter code wraps the generator function smartCode(generator) { var gen = generator(); var yieldedVal = gen.next(); if(yieldedVal.then) { //it's a promise!!! yieldedVal.then(gen.next); } }

//enter libraries like Co, Bluebird, Q...let's use Bluebird Promise.coroutine(function* () { var tweets = yield $.get('tweets.json'); console.log(tweets); })(); //Bluebird runs the generator, notices yield is a promise //so it waits on that promise, then passes it's value back to the generator when complete

//here, it runs them in sequence, waiting for each to complete before proceeding Promise.coroutine(function* () { var tweets = yield $.get('tweets.json'); var profile = yield $.get('profile.json'); var friends = yield $.get('friends.json'); console.log(tweets, profile, friends); })();

//if you want to run them at the same time, yield an object or an array Promise.coroutine(function* () { var data = yield { tweets: $.get('tweets.json'), profile: yield $.get('profile.json') }; console.log(data.tweets, data.profile); })();

Promise.coroutine(function* () { var [tweets, profile] = yield [$.get('tweets.json'), yield $.get('profile.json')]; console.log(tweets, profile); })();