Appcelerator和CommonJS模块(缓存和循环引用) [英] Appcelerator and CommonJS modules (caching and circular references)

问题描述

这是东西:

我正在使用CommonJS方式使我的移动(iPhone/Android)应用程序模块化.毫不奇怪.但是有一件事我只是无法理解.

I'm using the CommonJS way of making my mobile (iPhone/Android) application modular. No surprise there. But there's one thing that I just can't get my head around.

CommonJS让我创建STATIC私有变量，这使我可以轻松创建单例.至少我认为，这是因为获取require() d的文件的内容仅读取一次，然后每次都返回导出对象(仅初始化一次).

CommonJS lets me create STATIC private variables, which lets me create singletons at ease. This, I think at least, is because the contents of a file that gets require()d is read only once and then the exports object (which is initialized only once) is returned every time.

但是当我创建如下所示的循环引用时，所包含的模块内部的代码每次都会执行.

But when I create a circular reference as seen below, the code inside the included module is executed every time.

等待... 有趣的是，当我写这个问题时，我突然意识到对require()的任何调用都不会在下一个调用开始之前完成(因此，下面显示的堆栈溢出).

Wait... Funny thing is, while I'm writing this question, I suddenly realise that none of the calls to require() finish before the next one starts (hence the stack overflow demonstrated below).

关于我是否在轨道上的任何想法?到这里已经是凌晨5点了，所以就我而言，所有赌注都关闭了:D.

Any thoughts on whether I'm on track or not? It's past 5 AM over here, so all bets are off as far as I'm concerned :D.

示例:

参见这段代码，它定义了一个单例:

See this piece of code, it defines a singleton:

/* Singleton.js */

exports.getSingleton = getSingleton;

function getSingleton(name) {
  if (!instance) {
    instance = new Thing(name);
  }

  return instance;
}

function Thing(name) {
  this.name = name;
}

var instance;

我require()这样的文件:

var theFirstThing = require('Singleton').getSingleton('first');
Ti.API.info('first: ' + theFirstThing.name)

var possiblyAnotherOtherThing = require('Singleton').getSingleton('second');
Ti.API.info('second: ' + possiblyAnotherOtherThing.name);

输出为:

[DEBUG] loading: /path/to/sim/MyApp.app/app.js, resource: app_js
[DEBUG] loading: /path/to/sim/MyApp.app/Singleton.js, resource: Singleton_js
[INFO] first: first
[INFO] second: first

为什么为什么像下面这样的循环引用不起作用? (我本人可能已经对此回答了，如果您愿意，可以对此发表评论/回答.)

Why is it then that circular references like the following don't work? (I might have already ansered this myself, comment/answer on it if you like).

app.js

require('Banana');

Pinapple.js

require('Banana');

Banana.js

require('Pineapple');

因为输出是这样的

[DEBUG] loading: /path/to/simulator/MyApp.app/app.js, resource: app_js
[DEBUG] loading: /path/to/simulator/MyApp.app/Banana.js, resource: Banana_js
[DEBUG] loading: /path/to/simulator/MyApp.app/Pineapple.js, resource: Pineapple_js
[DEBUG] loading: /path/to/simulator/MyApp.app/Banana.js, resource: Banana_js
[DEBUG] loading: /path/to/simulator/MyApp.app/Pineapple.js, resource: Pineapple_js
[DEBUG] loading: /path/to/simulator/MyApp.app/Banana.js, resource: Banana_js
[DEBUG] loading: /path/to/simulator/MyApp.app/Pineapple.js, resource: Pineapple_js
[DEBUG] loading: /path/to/simulator/MyApp.app/Banana.js, resource: Banana_js

/* etcetera (total of 15 times back and forth) */

[DEBUG] loading: /path/to/simulator/MyApp.app/Pineapple.js, resource: Pineapple_js
[DEBUG] loading: /path/to/simulator/MyApp.app/Banana.js, resource: Banana_js
[DEBUG] loading: /path/to/simulator/MyApp.app/Pineapple.js, resource: Pineapple_js
[ERROR] Script Error = Maximum call stack size exceeded. (unknown file)

推荐答案

我也正在Appcelerator Titanium中使用CommonJS模块来构建移动应用程序.我为解决循环依赖问题所做的工作是:如果A和B是2个循环依赖的模块，则B中的require(A)，反之亦然在您实际需要使用它之前 .就我而言，仅当单击某个按钮时，我才需要B内部的A，因此我在按钮的click事件监听器中的B中放置了require(A).希望有帮助.

I too am using CommonJS modules in Appcelerator Titanium to build a mobile app. What I did to resolve the circular dependency problem was this: if A and B are the 2 circularly-dependent modules, require(A) in B, and vice-versa just before you actually need to use it. In my case, I needed A inside B only when a certain button got clicked, so I put a require(A) in B inside the button's click event listener. Hope that helps.

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