javascript - JavaScript 中双向生成器的实际使用

Question

来自 C# 世界，我很想了解 javascript 中双向生成器的一些实际用法。我可以理解生成器一般是如何有用的，但当涉及到双向生成器时则不然。我们可以将它与 RxJS 或类似的东西一起使用吗？你能解释一下可以使用它的任何模式/场景吗？

function* interrogate() {
   let name = yield "What is your name?";
   let color = yield "What is your favorite color?";
   return `${name}'s favorite color is ${color}.`;
}

let it = interrogate();
it.next();         // { value: "What is your name?", done: false }
it.next('Ethan');  // { value: "What is your favorite color?", done: false }
it.next('orange'); // { value: "Ethan's favorite color is orange.", done:true }

Answer 1

大卫沃尔什有一个 blog about ES6 Generators

他有一个例子

function *foo(x) {
    var y = 2 * (yield (x + 1));
    var z = yield (y / 3);
    return (x + y + z);
}

var it = foo( 5 );

// note: not sending anything into `next()` here
console.log( it.next() );       // { value:6, done:false }
console.log( it.next( 12 ) );   // { value:8, done:false }
console.log( it.next( 13 ) );   // { value:42, done:true }

但同样，用例与您的示例一样制造。

他在总结中说

It's natural to wonder what this new exotic toy is going to do practically for your code. There's a lot more to them, though. We've just scratched the surface. So we have to dive deeper before we can discover just how powerful they can/will be.

• How does error handling work?
• Can one generator call another generator?
• How does async coding work with generators?

Those questions, and more, will be covered in subsequent articles here, so stay tuned!

In a later blog他有以下片段(和其他一些片段)

// run (async) a generator to completion
// Note: simplified approach: no error handling here
function runGenerator(g) {
    var it = g(), ret;

    // asynchronously iterate over generator
    (function iterate(val){
        ret = it.next( val );

        if (!ret.done) {
            // poor man's "is it a promise?" test
            if ("then" in ret.value) {
                // wait on the promise
                ret.value.then( iterate );
            }
            // immediate value: just send right back in
            else {
                // avoid synchronous recursion
                setTimeout( function(){
                    iterate( ret.value );
                }, 0 );
            }
        }
    })();
}

runGenerator( function *main(){
    var result1 = yield request( "http://some.url.1" );
    var data = JSON.parse( result1 );

    var result2 = yield request( "http://some.url.2?id=" + data.id );
    var resp = JSON.parse( result2 );
    console.log( "The value you asked for: " + resp.value );
} );

这似乎更真实一些。

他总结

Put simply: a generator + yielded promise(s) combines the best of both worlds to get really powerful and elegant sync(-looking) async flow control expression capabilities. With simple wrapper utilities (which many libraries are already providing), we can automatically run our generators to completion, including sane and sync(-looking) error handling!