从函数返回值，具体取决于是否已解决Promise [英] Returning a value from a function depending on whether a Promise was resolved or not

问题描述

const dbConnection = require("../dbConnection");    

var task = function () {
    var response = "";
    dbConnection.then(function () {
        //do something here
        response = "some value";            
    })
    .catch(function () {
       response = new Error("could not connect to DB");
    });

    //I can't return response here because the promise is not yet resolved/rejected.
}

我正在使用别人编写的节点模块.它返回一个承诺.我想返回字符串还是 new Error()，具体取决于模块返回的Promise对象是否已解析.我该怎么办?

I'm using a node module that someone else wrote. It returns a promise. I want to return either a string or a new Error() depending on whether the Promise object returned by the module resolved or not. How can I do this?

我也不能在 finally()回调内部返回，因为 return 会应用于回调函数，而不是我的 task 函数.

I can't return inside the finally() callback either because that return would apply to the callback function not my task function.

推荐答案

const dbConnection = require("../dbConnection");    

var task = function () {
  var response = "";
  return dbConnection.then(function () {
    //do something here
    response = "some value";
    return response;
  })
  .catch(function () {
   response = new Error("could not connect to DB");
   return response;
  });
}

这将返回一个诺言，您可以随后将其链接.

This will return a promise which you can then chain.

使用promise的要点类似于使用回调.您不希望CPU坐在那里等待响应.

The point of using promises is similar to using callbacks. You don't want the CPU to sit there waiting for a response.

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