答应-`then()`不能按预期工作 [英] Promise - `then()` not works as expect

问题描述

我确实有2个功能.我与 promise 的 then()方法链接.但是我试图在第一个承诺发生后启动 second 函数.但是现在第二个函数调用成为第一个.该如何解决?

I do have 2 function. I am chaining with then() method for promise. But I am trying to initiate the second function after the first promise happend. But now the second function call as first. how to fix this?

或者我的代码有问题吗?

or any issue with my code?

这是我的尝试:

var getData = function(){
    return new Promise((resolve, reject) => {
    setTimeout(() => {
        resolve(42); //consoles as second
    }, 5000);
  })
}

var getDataMoreData = function(){
    return new Promise((resolve, reject) => {
    setTimeout(() => {
        resolve(43); //consoles as first
    }, 3000);
  })
}



getData().then((data)=> console.log('Data', data)).then(getDataMoreData().then((data)=> console.log('data--', data )));

实时演示

推荐答案

.然后接受 function 作为参数.当你做

.then accepts a function as a parameter. When you do

.then(getDataMoreData()
  .then((data) => console.log('data--', data))
);

，它立即调用 getDataMoreData()(期望它会返回可以放入promise链中的函数).但是 getDataMoreData 不会返回一个函数-它会返回一个Promise.

, it immediately calls getDataMoreData() (with the expectation that it will return a function that it can put into the promise chain). But getDataMoreData does not return a function - it returns a promise.

任何函数立即在 then 中调用，因为它试图构建 .then 承诺链.只需在 then 内列出函数变量，而不用调用它:

Any function calls immediately within a then get executed immediately, as it attempts to build the .then promise chain. Simply list the function variable inside the then instead of calling it:

var getData = function() {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve(42); 
    }, 500);
  })
}

var getDataMoreData = function() {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve(43); 
    }, 300);
  })
}



getData()
  .then((data) => console.log('Data', data))
  .then(getDataMoreData)
  .then((data) => console.log('data--', data));

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