JavaScript中的排序函数调用 - 回调是唯一的方法吗？ [英] sequencing function calls in javascript - are callbacks the only way?

问题描述

我通过各种主题阅读，例如这一个。

I read through various threads like this one for example.

但它真的逃脱了我如何完成以下：

But it really escapes me how to accomplish the following:

我有4个功能，另一个顺序。注意他们是不正确的顺序，让我的观点。我想要的结果将输出1，2，3，4'

I have 4 functions, and want them happen one after another in sequence. Notice they are in incorrect order, to get my point across. I want the result that will output "1, 2, 3, 4'

function firstFunction(){
  // some very time consuming asynchronous code...
  console.log('1');
}
function thirdFunction(){
  // definitely dont wanna do this until secondFunction is finished
  console.log('3');
}
function secondFunction(){
  // waits for firstFunction to be completed
  console.log('2');
}
function fourthFunction(){
  // last function, not executed until the other 3 are done.
  console.log('4');
}

我试图找出回调，但我会迷路：（

I tried to figure out callbacks but am getting lost :(

不是有一些简单的方法吗？像循环一个数组...

Isn't there some simple way to do this? Like looping through an array...

推荐答案

这是一个开始使用 jQuery Deferred 的好机会。

It's a great chance to start using jQuery Deferred.

除了基于回调的解决方案，代码是可读，灵活和高度可维护的。

Apart from the callbacks-based solution the code is readable, flexible and highly maintainable

http://jsfiddle.net/zerkms/zJhph/

function firstFunction(){
  var d = $.Deferred();
  // some very time consuming asynchronous code...
  setTimeout(function() {
    console.log('1');
    d.resolve();
  }, 1000);
  return d.promise();
}
function thirdFunction(){
  var d = $.Deferred();
  // definitely dont wanna do this until secondFunction is finished
  setTimeout(function() {
    console.log('3');
    d.resolve();
  }, 1000);
  return d.promise();
}
function secondFunction(){
  var d = $.Deferred();
  setTimeout(function() {
    console.log('2');
    d.resolve();
  }, 1000);
  return d.promise();
}
function fourthFunction(){
  var d = $.Deferred();
  // last function, not executed until the other 3 are done.
  setTimeout(function() {
    console.log('4');
    d.resolve();
  }, 1000);
  return d.promise();
}

firstFunction().pipe(secondFunction).pipe(thirdFunction).pipe(fourthFunction);​

PS：作为异步代码的一个例子，我使用了 setTimeout 。主要的是，在异步部分的结尾，你需要调用 d.resolve（）来继续链接方法。

PS: as an example of asynchronous code I've used setTimeout. The main thing is that in the end of the asynchronous part you need to call d.resolve() to continue chaining methods.

进一步阅读： http://joseoncode.com/2011/ 09/26 / a-walkthrough-jquery-deferred-and-promise /

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