Is it possible to use await without async in Js

问题:

Await is a amazing feature in es7.

However,everytime I use await I found that I have to define a async function and call this function.

Such as

    async function asy(){
        const [resCityGuess,resCityHot,resCityAll]=await Promise.all([
                        this.http.get('api/v1/cities?type=guess'),
                        this.http.get('api/v1/cities?type=hot'),
                        this.http.get('api/v1/cities?type=group')
        ])
        this.cityGuessName=resCityGuess.data.name;
        this.cityGuessId=resCityGuess.data.id;
        this.cityHot=resCityHot.data;
        this.cityAll=resCityAll.data;
    }
    asy.apply(this);

What I want is use await without async function such as

        // the async function definition is deleted
        const [resCityGuess,resCityHot,resCityAll]=await Promise.all([
                        this.http.get('api/v1/cities?type=guess'),
                        this.http.get('api/v1/cities?type=hot'),
                        this.http.get('api/v1/cities?type=group')
        ])
        this.cityGuessName=resCityGuess.data.name;
        this.cityGuessId=resCityGuess.data.id;
        this.cityHot=resCityHot.data;
        this.cityAll=resCityAll.data;
        // without call fn

I think define the function fn and call this fn is repeated sometimes so I want to know is it possible to optimize the situation？

Can I use await without async?

Thank you so much!

回答1:

No. The await operator only makes sense in an async function.

edit — to elaborate: the whole async and await deal can be thought of as being like a LISP macro. What that syntax does is inform the language interpretation system of what's going on, so that it can in effect synthesize a transformation of the surrounding code into a Promise-based sequence of callback requests.

Thus using the syntax is an implicit short-cut to coding up the explicit Promise stuff, with calls to .then() etc. The runtime has to know that a function is async because then it knows that async expressions inside the function need to be transformed to return Promises via a generator mechanism. And, for overlapping reasons, the async decoration on the function declaration tells the language that this is really a function that returns a Promise and that it needs to deal with that.

So, it's complicated. The process of improving and extending JavaScript has to account for the fact that there's an unimaginably massive amount of JavaScript code out in the world, and so in almost all cases no new feature can cause a page untouched since 2002 to fail.