从setTimeout获取返回值 [英] Get return value from setTimeout

问题描述

我只想从setTimeout获取返回值，但我得到的是该函数的整个文本格式？

I just want to get the return value from setTimeout but what i get is a whole text format of the function?

function x () {
    setTimeout(y = function () {
        return 'done';
    }, 1000);
    return y;
}

console.log(x());

推荐答案

您需要使用Promises。它们是在ES6中提供，但可以是polyfilled 非常轻松：

You need to use Promises for this. They are available in ES6 but can be polyfilled quite easily:

function x() {
   var promise = new Promise(function(resolve, reject) {
     window.setTimeout(function() {
       resolve('done!');
     });
   });
   return promise;
}

x().then(function(done) {
  console.log(done); // --> 'done!'
});

async / 等待在ES2017中如果在 async 函数内变得更好：

With async/await in ES2017 it becomes nicer if inside an async function:

async function() {
  const result = await x();
  console.log(result); // --> 'done!';
}

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