返回其自身实例的Object [英] An Object that returns an instance of itself

问题描述

背景：我的最新项目无法使用大型图书馆，这让我很难过。我希望从任何库中获得一些东西，例如缺少的函数 addClass ， hasClass ， removeClass ，兼容 addEventListener 等等所以我创建了一个小对象，我想在其他时间看到一些意见，但是我在设置它时遇到了一些麻烦。

Background: My latest project cannot use a large library, which saddens me. There are a few things that I would like to have from any library such as the missing functions addClass, hasClass, removeClass, compatible addEventListener, etc. So I created a little object which I'd like some opinions on some other time, but I'm having a little bit of trouble setting it up how I'd like.

为方便使用，我希望对象在创建时返回自己的新实例。

鉴于：

 $ = function() {
    this.name = "levi";

    return this;
};

console.log($());

我们得到DOMWindow而不是 $ 因为JavaScript中的这个的古怪性质。 对我来说更奇怪的是 console.log（new $（）。name）正确返回levi。如果此绑定到窗口，为什么该对象正确获取值？。我们可以添加新的 console.log（new $（）），它可以工作。但是，我不想每次都写新的。所以我试过了：

We get DOMWindow instead of $ because of the quirky nature of this in JavaScript. What's more strange to me is that console.log(new $().name) properly returns "levi". If this is bound to window, why did the object properly get the value?. We could just add new console.log(new $()) and it works. However, I don't want to write new everytime. So I tried:

$ = function() {
    var obj = function() {
        this.name = "levi";
    };

    return new obj();
};

console.log($());

这给了我想要的东西，但似乎有点不必将对象包装在函数内部创造它。此外，返回的对象是 obj 而不是 $ 。比较测试会失败。

Which gives me what I want, but it seems a bit unnecessary to wrap the object inside of a function which creates it. Further more, the returned object is obj and not $. Comparison tests would fail.

还有什么方法可以做到这一点？有更优雅的解决方案吗？我对重新思考整个过程没有任何疑虑。我认为自己非常擅长使用JavaScript，但创建新的JavaScript是我非常新的。

What are some other ways this can be done? Is there a more elegant solution? I have no qualms about rethinking my entire process. I consider myself pretty good at using JavaScript, but creating new JavaScript is something I am very new to.

有没有人看到以下解决方案有什么问题吗？

Does anyone see anything wrong with the following solution?

$a = function() {};

$ = function() {
    if (!(this instanceof $)) {
        return new $();
    }

    this.name = "levi";

    return this;
};

//helper function
var log = function(message) {
    document.write((message ? message : '') + "<br/>");
};

log("$().name == window.name: " + ($().name == window.name)); //false
log("$().name: " + $().name); //levi
log("window.name: " + window.name); //result

log();

log("$a instanceof $: " + ($a instanceof $)); //false
log("typeof $a: " + (typeof $a)); //function
log("typeof $: " + (typeof $)); //function

它似乎在我的所有测试中都有效。

It appears to be working in all my tests.

推荐答案

做你想做的最简单的方法是（我认为）：

The most simple way to do what you want would be (I think):

$ = function(){
    if (!(this instanceof $)){
     return new $;
    }
    this.name = 'levi'; 
    return this;
}

事实上只返回这个不会创建$的实例，因为这个的创建方式是作为常规执行 $ function：在这种情况下，这个的值指向全局对象（在浏览器中： window ，实际调用执行 $（）与窗口相同。$（））。这可以说是javascript生活的事实。 console.log（new $（）。name）显示正确值的事实是因为您将该函数作为构造函数调用，该构造函数返回该构造函数的实例（即 $ 的新实例。但是 console.log（$（）。name）也将打印'levi'，因为它返回属性为 name ，即 window.name 。尝试 $（）; console.log（name），你会看到 name 现在是一个全局变量。因此，如果您不想每次都使用 new 关键字，请检查您的函数是作为常规函数调用，还是作为实例的构造函数调用（ === instanceof $ ）在构造函数中。使用上面的方法实例构造函数，无论是否使用 new 进行实例化，总是 $

The fact that just returning this doesn't create an instance of $ is because of the way this is created executing $ as a regular function: in that case the value of this points to the global object (within a browser: window, actually calling executing $() is the same as window.$()). It's a fact of javascript life so to speak. The fact that console.log(new $().name) shows the right value is because you call the function as a constructor, which returns an instance of that constructor (i.e. an new instance of $). But console.log($().name) will also print 'levi', because it returns the global object with property name, i.e. window.name. try $(); console.log(name) and you'll see name is a global variable now. So if you don't want to use the new keyword every time, check if your function is called as a regular function, or as a constructor for an instance (=== instanceof $) within the constructor function. With the above method an instances constructor, no matter if it's instantiated with or without new will allways be $

也许您应该将问题的标题改为：'一个返回自身实例的对象[构造函数] '

Maybe you should rephrase the title of your question to: 'An Object [constructor] that returns an instance of itself'

也许此博客文章可以减轻额外的光。

Maybe this blog entry can shed extra light.

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