我得到:[ts]'Promise'仅指类型，但在此处被用作值 [英] I get: [ts] 'Promise' only refers to a type, but is being used as a value here

问题描述

我正在学习Angular2课程并继续学习.到目前为止，我在所有其他练习中所做的所有工作都运转良好，直到我创建了此自定义验证器和此Promise代码为止.对我来说毫无意义，为什么现在会发生这种情况.

I'm taking an Angular2 course and following along. Everything I have been doing thus far for all the other exercise has worked fine until I got to creating this custom validator and this Promise code. Makes no sense to me why this would occur now.

我得到:[ts]'Promise'仅指一种类型，但是在这里被用作值.

I get: [ts] 'Promise' only refers to a type, but is being used as a value here.

似乎无法解决此问题.即使没有添加setTimeout函数，我也会收到错误消息.

Can't seem to resolve this. I get my error even without adding in the setTimeout function.

根据其他人的建议.我添加到tsconfig.json: "compilerOptions":{ ... "types":["core-js"] }

Per a suggestion from someone elsewhere. I added to the tsconfig.json: "compilerOptions": { ... "types" : [ "core-js" ] }

但是我仍然会收到错误消息.

But I still get the error.

使用Visual Studio代码:1.10.1版. 操作系统:Windows 10 Pro.

Using Visual Studio code: Version 1.10.1. OS: Windows 10 Pro.

这是我的代码:

import {Control} from 'angular2/common';

export class UsernameValidators 
{
    static shouldBeUnique(control: Control) 
    {
       return new Promise((resolve, reject) =>
       {            
          setTimeout(function()
          {
             if (control.value == "Dan")
                resolve({ shouldBeUnique: true });
             else
                resolve(null);
          }, 1000);
       });
   }
}

这是我正在上的课程，以及被指示要做的事情的屏幕截图.智能感知与我的不同.效果很好，他们没有得到我得到的错误.

Here's the course that I am taking and a screen shot of what I am being instructed to do. The intelliSense is different from mine. It works fine and they do not get the error I get.

这是课程的最终结果.

推荐答案

您需要定位ES6，否则请使用诸如bluebird之类的polyfill库.如果要在编译器输出中定位ES5，则它将失败，因为ES5没有承诺.

You need to target ES6, or else use a polyfill library like bluebird. If you are targeting ES5 in the compiler output, then it will fail like this because ES5 has no Promises.

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