如何在JavaScript中设置函数执行顺序以使用回调函数？ [英] How to set function execute order to using callback function in JavaScript?

问题描述

我想处理函数执行顺序以使用回调。其实我正在学习Node.js.由于它的异步，我很难处理过程。无论如何，有3个函数有回调，

I want to handle functions execute order to using callbacks. Actually I'm learning Node.js. Because of its async, It's difficult to me to handle process. Anyway, There are 3 function that has callback,

function first(callback){
    console.log("First");
    callback;
}

function second(callback){
    console.log("Second");
    callback;
}


function third(callback){
    console.log("Third");
}

// Let's run it!

first(second(third));

// result 

Second
First

我不明白为什么结果如此。我预计如下：

I don't understand why the result is. I expected below:

First
Second
Third

有什么问题？我怎么能正确地做到这一点？在Node.js中，人们通常使用回调来处理函数执行顺序吗？我觉得这有点复杂。不是吗？

What's problem? How could I do it correctly? In Node.js, Do people usually handle functions excute order by using callbacks? that is little complex I think. Isn't it?

推荐答案

如其他答案所述，

first(second(third));

这不符合你的想法。

我认为你真正打算做的是：

I think what you actually meant to do was this:

first(function(){
    second(function(){
        third(function(){
            // ...
        });
    });
});

在ES6（节点4+）语法中它将是：

In ES6 (Node 4+) syntax it'll be:

first(() => second(() => third()));

但我更喜欢的是一种使用Promises的方法

But what I prefer is an approach that uses Promises

function first(){
    return new Promise(function(resolve, reject){
        console.log("First");
        resolve();
    });
}

function second(){
    return new Promise(function(resolve, reject){
        console.log("Second");
        resolve();
    });
}

function third(){
    return new Promise(function(resolve, reject){
        console.log("Third");
        resolve();
    });
}

这完全摆脱了回调，让人更了解实际的控制流程：

This gets rid of callbacks altogether, and makes more sense of the actual control flow:

first()
.then(second)
.then(third);

^{结帐这篇关于承诺的文章}

使用ES7语法（babel / typescript）它只会变成：

And with the ES7 syntax (babel/typescript) it simply becomes:

async function first(){
    console.log("First");
}
// async function second...
// async function third...

await first();
await second();
await third();

^{在async / await上查看本文}

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