javascript async/await and promise [英] javascript async/await and promise

问题描述

我很难理解异步/等待的工作方式，我必须编写一个包含以下三个功能的程序: func1 func2 和 concatenated . func1 将一个字符串作为参数，并在延迟5秒后返回相同的字符串， func2 是一个 async 函数，该函数还将一个字符串作为一个参数并返回相同的字符串. concatenated 是一个函数，它使用两个字符串(s1，s2)作为参数，并使用上述两个函数((func1(s1)和func2(s2))))在5秒后返回其串联结果.因此，如果我们将("hello"，"world")传递给 concatenated ，它将返回 hello world .我的代码是:

I'm having a hard time understanding how async/await works.I have to make a program which contains three functions: func1 func2 and concatenated. func1 takes a string as an argument and returns the same string after 5 seconds of delay, func2 is an async function which also takes a string as an argument and returns the same string. concatenated is a function that takes two strings (s1,s2) as arguments and uses the above two functions((func1(s1) and func2(s2))) to return their concatenated result after 5 seconds. So if we pass ("hello"," world") to concatenated it should return hello world. My code is:

function func1(x) {
return new Promise(resolve => {
setTimeout(() => {
  resolve(x);
    }, 5000);
  });
 }

async function func2(x) {
const a = await func1(x);
return a;
}

function concatenated(a,b){
  const c = func2(a).then(result =>{console.log(result)});
  const d = func2(b).then(result =>{console.log(result)});
  return (c+d) ;
} 

concatenated("hello"," world")

此代码仅给我:
你好世界

我该如何纠正?

推荐答案

问题是您从 concatenated 函数返回的语句将同步运行.这也意味着 c 和 d 仍然是承诺.

The problem is that your return statement from the concatenated function will be run synchronously. This also means that c and d will still be promises.

可能的解决方案是:

async function concatenated(a,b){
  const c = await func2(a);
  const d = await func2(b);

  return (c+d);
} 

concatenated("hello", " world").then(result => {
    console.log(result); // hello world
})

请注意，异步功能将始终返回承诺.

Notice that an async function will always return a promise.

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