Why does ES2017 introduce async / await when ES6 already has generators?

Question

While reading about asyncand awaitI noticed that this is almost the equivalent of generator functions. Consider this snippet from TypeScript Deep Dive :

Waiting for Async

(...)

// Not actual code. A thought experiment
async function foo() {
    try {
        var val = await getMeAPromise();
        console.log(val);
    }
    catch(err) {
        console.log('Error: ', err.message);
    }
}

(...)

JavaScript generated

You do not have to understand this, but it is quite simple if you read about generators. A function foocan simply be wrapped as follows:

const foo = wrapToReturnPromise(function* () {
    try {
        var val = yield getMeAPromise();
        console.log(val);
    }
    catch(err) {
        console.log('Error: ', err.message);
    }
});

where it wrapToReturnPromisesimply performs the function of a generator to receive generatorand then use generator.next(), if the value is equal promise, it will be then+ a catchpromise and, depending on the result, call genertor.next(result)or genertor.throw(error). What is it!

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Answer 1

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