了解承诺:需要结合多个结果 [英] Understanding Promises: Need to combine multiple results

问题描述

我如何处理多个Promise的结果? 在DoNext中说出DoA的结果a和DoB的结果

How do I process the results of more than one Promise? Say the results a of DoA and b of DoB in DoNext

我阅读了 https://developer.mozilla.org/de /docs/Web/JavaScript/Guide/Using_promises 它引入了"then"语法，该语法应取代"doom的回调金字塔"，但我不理解以下内容:

I read https://developer.mozilla.org/de/docs/Web/JavaScript/Guide/Using_promises It introduces the "then"-Syntax which is supposed to replace the "callback pyramid of doom" however I don't understand the following:

DoA.then(function(a){
    return DoB(a)
})
.then(function(b){
    DoNext(a,b);
})

在DoNext的调用中，a是未知的.我知道这是因为a仅在第2行的匿名函数中定义.但是，在厄运的回调金字塔"中，我可以访问a，因为在该模式中，DoNext位于匿名函数内，该函数是DoA的成功回调. 我该如何在then-Syntax中处理这个问题?

In the call of DoNext, a is unknown. I understand that this is because a is only defined in the anonymous function in line 2. However in the "callback pyramid of doom" I can access a, because in that pattern DoNext is within the anonymous function that is the success callback of DoA. How do I handle this in then-Syntax?

推荐答案

处理多种Promise情况有多种方法.

There are multiple ways of handling multiple Promise situation.

1-链承诺(虽然很丑)

1- Chain Promise (ugly though)

DoA.then(a => {
    DoB(a).then(.....)

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

2- Promise.all()

var promise1 = Promise.resolve(3);
var promise2 = 42;
var promise3 = new Promise(function(resolve, reject) {
  setTimeout(resolve, 100, 'foo');
});

Promise.all([promise1, promise2, promise3]).then(function(values) {
  console.log(values);
});
// expected output: Array [3, 42, "foo"]

3- 异步功能(但请阅读详细信息)

3- async function (but read the details)

(async () => {

  const a = await DoA(); // DoA must be a Promise
  const b = await DoB(a); // DoB must be a Promise
  // rest of the code

})();

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