freeCodeCamp/curriculum/challenges/chinese/02-javascript-algorithms-and-data-structures/es6/handle-a-rejected-promise-with-catch.md

id	challengeType	forumTopicId	title
5cdafbe72913098997531682	1	301204	在 catch 中处理 Promise 失败的情况

Description

当 promise 失败时会调用 catch 方法。当 promise 的 reject 方法执行时会直接调用。用法如下：

myPromise.catch(error => {
  // do something with the error.
});

error 是传入 reject 方法的参数。

注意： then 和 catch 方法可以在 promise 后面链式调用。

Instructions

给 promise 添加 catch 方法。用 error 做为回调函数的参数并把 error 打印到控制台。

Tests

tests:
  - text: 应该在 promise 上调用 <code>catch</code> 方法。
    testString: assert(codeWithoutSpaces.match(/(makeServerRequest|\))\.catch\(/g));
  - text: <code>catch</code> 方法应该有一个回调函数，函数参数为<code>error</code>。
    testString: assert(errorIsParameter);
  - text: 应该打印<code>error</code>到控制台。
    testString: assert(errorIsParameter && codeWithoutSpaces.match(/\.catch\(.*?error.*?console.log\(error\).*?\)/));

Challenge Seed

const makeServerRequest = new Promise((resolve, reject) => {
  // responseFromServer is set to false to represent an unsuccessful response from a server
  let responseFromServer = false;
	
  if(responseFromServer) {
    resolve("We got the data");
  } else {	
    reject("Data not received");
  }
});

makeServerRequest.then(result => {
  console.log(result);
});

After Test

const codeWithoutSpaces = code.replace(/\s/g, '');
const errorIsParameter = /\.catch\((function\(error\){|error|\(error\)=>)/.test(codeWithoutSpaces);

Solution

const makeServerRequest = new Promise((resolve, reject) => {
  // responseFromServer is set to false to represent an unsuccessful response from a server
  let responseFromServer = false;
	
  if(responseFromServer) {
    resolve("We got the data");
  } else {	
    reject("Data not received");
  }
});

makeServerRequest.then(result => {
  console.log(result);
});

makeServerRequest.catch(error => {
  console.log(error);
});