Javascript：扩展函数 [英] Javascript: Extend a Function

问题描述

类似这样的内容：

$ b $我想要的主要原因是我想扩展我的初始化函数。 b

  // main.js 
 
 window.onload = init（）; 
函数init（）{
 doSomething（）; 
 
 
 // extend.js 
 
函数扩展init（）{
 doSomethingHereToo（）; 
 
 
 
 
 
 $ b所以我想扩展一个函数，比如我在PHP中扩展一个类。 / p> 
 
 
我也想从其他文件扩展它，例如我在 main.js 和 extended.js中的扩展函数。
解决方案
更广泛地了解你实际上想要做什么以及你在做什么的背景，我相信我们可以给你一个比你的问题的文字更好的答案。 / p> 
 
 
但是，这是一个字面上的答案：
 
 
如果您将这些函数分配给某处的某个属性，原来的功能，并把你的替换物业，而不是：
  // main.js中的原始代码
 var theProperty = init; 
 
函数init（）{
 doSomething（）; 
} 
 
 //通过在extended.js中替换和包装来扩展它
 theProperty =（function（old）{
 function extendsInit（）{
 old（）; 
 doSomething（）; 
} 
 
 return extendsInit; 
}）（theProperty）; 
  
如果你的函数不在一个对象上，你可能想把它放在那里方便以上。例如：
 
 
  //在main.js中
 var MyLibrary =（function（）{
 var publicSymbols = {}; 
 
 publicSymbols.init = init; 
函数init（）{
} 
 
 return publicSymbols; 
}） （）; 
 
 //在extended.js 
（function（）{
 var oldInit = MyLibrary.init; 
 MyLibrary.init = extendedInit; 
 function extendedInit （）{
 oldInit.apply（MyLibrary）; //在`init`使用`this`的情况下使用#apply 
 doSomething（）; 
} 
}）（）; 
  
但是这样更好的方法来做到这一点。例如，提供注册 init 函数的方法。
  / / in main.js 
 var MyLibrary =（function（）{
 var publicSymbols = {}，
 initfunctions = []; 
 
 publicSymbols.init = init; 
函数init（）{
 var funcs = initFunctions; 
 
 initFunctions = undefined; 
 
 for（index = 0; index< funcs.length ; ++ index）{
 try {funcs [index]（）;} catch（e）{} 
 
 
 $ b publicSymbols.addInitFunction = addInitFunction; 
函数addInitFunction（f）{
 if（initFunctions）{
 // Init尚未运行，记住它
 initFunctions.push（f）; 
} 
 else {
 //`init`已经运行，几乎立即调用它
 //但是*异步*（因此调用者从不会同时看到
 //调用）
套超时（f，0）; 
} 
} 
 
 return publicSymbols; 
}）（）; 
  
 （以上大部分内容可以写得更简洁一点，但我想用清晰的名字，比如 publicSymbols 而不是我通常的 pubs 或者匿名对象文字。想要匿名功能，但我不太在乎匿名功能。） 
 
The main reason why I want it is that I want to extend my initialize function.

Something like this:
// main.js

window.onload = init();
function init(){
     doSomething();
}

// extend.js

function extends init(){
    doSomethingHereToo();
}
So I want to extend a function like I extend a class in PHP.

And I would like to extend it from other files too, so for example I have the original init function in main.js and the extended function in extended.js.
解决方案
With a wider view of what you're actually trying to do and the context in which you're doing it, I'm sure we could give you a better answer than the literal answer to your question.

But here's a literal answer:

If you're assigning these functions to some property somewhere, you can wrap the original function and put your replacement on the property instead:
// Original code in main.js
var theProperty = init;

function init(){
     doSomething();
}

// Extending it by replacing and wrapping, in extended.js
theProperty = (function(old) {
    function extendsInit() {
        old();
        doSomething();
    }

    return extendsInit;
})(theProperty);
If your functions aren't already on an object, you'd probably want to put them there to facilitate the above. For instance:
// In main.js
var MyLibrary = (function() {
    var publicSymbols = {};

    publicSymbols.init = init;
    function init() {
    }

    return publicSymbols;
})();

// In extended.js
(function() {
    var oldInit = MyLibrary.init;
    MyLibrary.init = extendedInit;
    function extendedInit() {
        oldInit.apply(MyLibrary); // Use #apply in case `init` uses `this`
        doSomething();
    }
})();
But there are such better ways to do that. Like for instance, providing a means of registering init functions.
// In main.js
var MyLibrary = (function() {
    var publicSymbols = {},
        initfunctions = [];

    publicSymbols.init = init;
    function init() {
        var funcs = initFunctions;

        initFunctions = undefined;

        for (index = 0; index < funcs.length; ++index) {
            try { funcs[index](); } catch (e) { }
        }
    }

    publicSymbols.addInitFunction = addInitFunction;
    function addInitFunction(f) {
        if (initFunctions) {
            // Init hasn't run yet, rememeber it
            initFunctions.push(f);
        }
        else {
            // `init` has already run, call it almost immediately
            // but *asynchronously* (so the caller never sees the
            // call synchronously)
            setTimeout(f, 0);
        }
    }

    return publicSymbols;
})();
(Much of the above could be written a bit more compactly, but I wanted to use clear names like publicSymbols rather than my usual pubs or anonymous object literal. You can write it a lot more compactly if you want to have anonymous functions, but I don't much care for anonymous functions.)

                        
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