异步的NodeJS混乱 [英] Nodejs asynchronous confusion

问题描述

我似乎无法掌握如何维持与异步的NodeJS控制流。所有嵌套使得code很辛苦在我看来，阅读。我是个新手，所以我可能因小失大。

什么是错的只是编码这样的事情...

 函数第一个（）{
    VAR对象= {
        aProperty：'东西'，
        anArray：['HTML'，'HTML'];
    };
    第二（目标）;
}函数的第二（对象）{
    对于（VAR I = 0; I＆LT; object.anArray.length;我++）{
        第三个（object.anArray [I]）;
    };
}第三个功能（HTML）{
    //解析HTML
}
第一（）;
 

解决方案

大画面的是，任何I / O是非阻塞的，并在你的JavaScript异步执行;所以，如果你做任何数据库查询，从插座（在HTTP服务器如）读取数据，读取或写入文件，磁盘，等等，你的有无的使用异步code。这是必要的，因为事件循环是单线程的，如果I / O是不是不堵塞，你的程序将在执行其暂停。

您的可以的结构中的code等，有筑巢少;例如：

 变种FS =要求（FS）;
VAR的mysql =要求（'some_mysql_library'）;fs.readFile（'/我的/ file.txt的'，'UTF8'，processFile）;功能processFile（ERR，数据）{
  mysql.query（INSERT INTO TBL SET TXT ='+数据+'，doneWithSql）;
}功能doneWithSql（ERR，结果）{
  如果（ERR）{
    的console.log（有您的查询的问题）;
  }其他{
    的console.log（以下简称查询成功。）;
  }
}
 

也有流量控制库如异步（我个人的选择），以帮助避免大量的嵌套回调。

您可能感兴趣的此截屏我关于这个问题的创建。

I can't seem to grasp how to maintain async control flow with NodeJs. All of the nesting makes the code very hard to read in my opinion. I'm a novice, so I'm probably missing the big picture.

What is wrong with simply coding something like this...

function first() {
    var object = {
        aProperty: 'stuff',
        anArray: ['html', 'html'];
    };
    second(object);
}

function second(object) {
    for (var i = 0; i < object.anArray.length; i++) {
        third(object.anArray[i]);
    };
}

function third(html) {
    // Parse html
}
first();

解决方案

The "big picture" is that any I/O is non-blocking and is performed asynchronously in your JavaScript; so if you do any database lookups, read data from a socket (e.g. in an HTTP server), read or write files to the disk, etc., you have to use asynchronous code. This is necessary as the event loop is a single thread, and if I/O wasn't non-blocking, your program would pause while performing it.

You can structure your code such that there is less nesting; for example:

var fs = require('fs');
var mysql = require('some_mysql_library');

fs.readFile('/my/file.txt', 'utf8', processFile);

function processFile(err, data) {
  mysql.query("INSERT INTO tbl SET txt = '" + data + "'", doneWithSql);
}

function doneWithSql(err, results) {
  if(err) {
    console.log("There was a problem with your query");
  } else {
    console.log("The query was successful.");
  }
}

There are also flow control libraries like async (my personal choice) to help avoid lots of nested callbacks.

You may be interested in this screencast I created on the subject.

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