Difference between async/await and ES6 yield with generators

Question

I was just reading this fantastic article «Generators» and it clearly highlights this function, which is a helper function for handling generator functions:

Answer 1

Well, it turns out that there is a very close relationship between async/await and generators. And I believe async/await will always be built on generators. If you look at the way Babel transpiles async/await:

Babel takes this:

this.it('is a test', async function () {

    const foo = await 3;
    const bar = await new Promise(resolve => resolve('7'));
    const baz = bar * foo;
    console.log(baz);

});

and turns it into this

function _asyncToGenerator(fn) {
    return function () {
        var gen = fn.apply(this, arguments);
        return new Promise(function (resolve, reject) {
            function step(key, arg) {
                try {
                    var info = gen[key](arg);
                    var value = info.value;
                } catch (error) {
                    reject(error);
                    return;
                }
                if (info.done) {
                    resolve(value);
                } else {
                    return Promise.resolve(value).then(function (value) {
                        return step("next", value);
                    }, function (err) {
                        return step("throw", err);
                    });
                }
            }

            return step("next");
        });
    };
}


this.it('is a test', _asyncToGenerator(function* () {   // << now it's a generator

    const foo = yield 3;    //  <<< now it's yield, not await
    const bar = yield new Promise(resolve => resolve(7));
    const baz = bar * foo;
    console.log(baz);

}));

you do the math.

This makes it look like the async keyword is just that wrapper function, but if that's the case then await just gets turned into yield, there will probably be a bit more to the picture later on when they become native.

You can see more of an explanation for this here: https://www.promisejs.org/generators/