(ES6)类(ES2017)async/await getter

Question

是否可以让ES6类getter从ES2017 await/async函数返回一个值.

class Foo {
    async get bar() {
        var result = await someAsyncOperation();

        return result;
    }
}

function someAsyncOperation() {
    return new Promise(function(resolve) {
        setTimeout(function() {
            resolve('baz');
        }, 1000);
    });
}

var foo = new Foo();

foo.bar.should.equal('baz');

Answer 1

你可以这样做

class Foo {
    get bar() {
        return (async () => {
            return await someAsyncOperation();
        })();
    }
}

这也是一样的

class Foo {
    get bar() {
        return new Promise((resolve, reject) => {
            someAsyncOperation().then(result => {
                resolve(result);
            });
        })
    }
}

Answer 2

你只能await承诺,async功能将自己返回承诺.
当然,吸气剂也可以产生这样的承诺,与正常值没有区别.

Answer 3

您可以await在调用方获得该值。

class Foo {
    get bar() {
        return someAsyncOperation();
    }
}
async function test(){
  let foo = new Foo, val = await foo.bar;
  val.should.equal('baz');
}