Question

我对此代码有疑问：

var request = require('request-promise');

class Test{

constructor(){

}

async Start(){
    var response = await this.getResponse();
    await console.log(response);
}

async getResponse(){
    var options = {
        uri: "https://www.google.com"
    }

    var response = await request(options);

    setTimeout(function(){
        return response;
    },1000);
}

}

module.exports = Test;

当我运行Start（）时，控制台记录“未定义”，但这是为什么呢？我知道我在返回上设置了1秒的延迟，但是代码不应该等到返回时吗？因为等待？

P.S：延迟是为了模拟正在处理的响应数据。

Answer 1

如果您确实想在1000后发送响应，请使用Promise，否则无需这样做。

var request = require('request-promise');

class Test{

constructor(){

}

async Start(){
    var response = await this.getResponse();
    await console.log(response);
}

async getResponse(){
    var options = {
        uri: "https://www.google.com"
    }

    var response = await request(options);
    return new Promise((resolve) => {
    setTimeout(() => resolve(response), 1000)
    })
 }

}

module.exports = Test;

Answer 2

您不能将“ return”放在另一个函数的内部，并且不能期望它返回到外部函数。（最大的问题）

async getResponse(){
    setTimeout(function(){
        return "Test";
    },1000);
    return undefined; // line is basically what is here when you don't return anything
}

await getReponse(); // returns undefined, NOT "Test".

您可以改为这样编写代码：

  const delay = time => new Promise(res=>setTimeout(res,time));
  class Test{
    constructor(){
    }

    async Start(){
        var response = await this.getResponse();
        console.log(response); // await not needed here.
    }

    async getResponse(){
        var options = {
            uri: "https://www.google.com"
        }

        var response = await request(options);

        await delay(1000); // since we're using async functions, we can "await" a promise
        return response; 
        // previous code would return "undefined" when after it called setTimeout
    }

  }

  module.exports = Test;

Answer 3

您为什么不只使用承诺：

var request = require('request-promise');

class Test{

    constructor(){

    }

    Start(){
        this.getResponse()
            .then(response => console.log(response))
            .catch(err => console.log(err));
    }

    getResponse(){
        var options = {
            uri: "https://www.google.com"
        }

        return request(options);
    }

}

module.exports = Test;

Node.js异步/延迟等待

3 个答案: