Code snippets for Javascript generators and asynchronous code presentation. Based on http://eyalarubas.com/javascript-generators-and-callbacks.html

1.generator_example.js

// generate a series of even numbers,
// but be able to to reverse the order of iteration

function * generateEvens(start) {
    var dir = 1; // up
    if (start % 2 !== 0) start++;
    while (true) {
        var tmp = yield start;
        if (tmp === 'up') dir = 1;
        if (tmp === 'down') dir = -1;
        start += dir * 2;
    }
}

var evens = generateEvens(5);

console.log(    evens.next().value          ); // 6
console.log(    evens.next().value          ); // 8
console.log(    evens.next('down').value    ); // 6
console.log(    evens.next().value          ); // 4
console.log(    evens.next().value          ); // 2
console.log(    evens.next('up').value      ); // 4
console.log(    evens.next().value          ); // 6

2.async_classic.js

// simulate async database calls with 'getFoo' and 'getBar'.
// retrieve 'foo' and 'bar' and print to console.

var foo, bar;

function getFoo(callback) {
    setTimeout(function() {
        callback('hello');
    }, 200);
}

function getBar(callback) {
    setTimeout(function() {
        callback('world');
    }, 200);
}

getFoo(function(val) {
    foo = val
    getBar(function(val) {
        bar = val;
        console.log(foo, bar); // hello world
    });
});

3.async_yield_almost.js

// simulate async database calls with 'getFoo' and 'getBar'.
// retrieve 'foo' and 'bar' and print to console.
// try to use a generator to pause execution.
// WILL NOT WORK. SEE '4.async_yield.js'

function getFoo(callback) {
    setTimeout(function() {
        callback('hello');
    }, 200);
}

function getBar(callback) {
    setTimeout(function() {
        callback('world');
    }, 200);
}

function * run (){
    var foo = yield getFoo();
    var bar = yield getBar();
    console.log(foo,bar);
};

run();

4.async_yield.js

// simulate async database calls with 'getFoo' and 'getBar'.
// retrieve 'foo' and 'bar' and print to console.
// use a generator to pause execution.

function getFoo(callback) {
    setTimeout(function() {
        callback('hello');
    }, 200);
}

function getBar(callback) {
    setTimeout(function() {
        callback('world');
    }, 200);
}

function resume(value) {
    r.next(value);
}

function * run(resume) {
    var foo = yield getFoo(resume);
    var bar = yield getBar(resume);
    console.log(foo, bar); // hello world
}

var r = run(resume);
r.next(); // start