jQuery如何表现得像一个对象和一个函数？

问题描述

jQuery 或 $ 似乎是一个函数：

typeof $; // "function"

它就像一个：

$('div').removeClass(); // $ constructs a new object with some methods like removeClass

但是当我删除函数括号时它会表现出来像一个对象：

But when I drop the function parentheses it behaves like an object:

$.each(/* parameters */); // $ is an object with some methods like each

我想知道这是怎么回事以及如何将这种行为实现到我自己的函数中。

I'd like to know how this is possible and how I can implement this behaviour to my own functions.

推荐答案

函数也是对象，所以 $ .each 可以用与Object类似的方式定义。

Functions are also objects, so $.each can be defined in a similar way as an Object.

JavaScript是一种原型语言。对于jQuery，这意味着 $ 的每个实例都从 jQuery.prototype 继承方法。

JavaScript is a prototypical language. For jQuery, this means that every instance of $ inherits methods from jQuery.prototype.

一个非常粗略的演示，以实现类似的行为：

A very rough demo, to achieve the similar behaviour:

(function() { // Closure to not leak local variables to the global scope
    function f(a, b) {
        //Do something
    }
    // Prototype. All properties of f.prototype are inherited by instances of f.
    // An instance of f can be obtained by:    new f, new f(), Object.create(f)
    f.prototype.removeClass = function(a) {
        return a;
    };
    function $(a, b) {
        return new f(a, b); // <--- "new f" !
    }
    $.each = function(a) {
        alert(a);
    };
    window.$ = $; // Publish public methods
})();

//Tests (these do not represent jQuery methods):
$.each("Foo");                   // Alerts "Foo" (alert defined at $.each)
alert($().removeClass('Blabla'));// Alerts "Blabla"

注释

jQuery的根方法定义如下（仅显示相关部分）：

Notes

jQuery's root method is defined as follows (only relevants parts are shown):

(function(win) {
    var jQuery = function (selector, context) {
        return new jQuery.fn.init(selector, context, rootjQuery);
    };
    //$.fn = jQuery.fn is a shorthand for defining "jQuery plugins".
    jQuery.fn = jQuery.prototype = {
        constructor: jQuery,
        init: function( /* ..parameters.. */ ) {
            //.... sets default properties...
        }
        //....other methods, such as size, get, etc...
        //.... other properties, such as selector, length, etc...
    };
    jQuery.fn.removeClass = function() { // (Actually via jQuery.fn.extend)
        // ... method logic...
    };  //...lots of other stuff...

    win.$ = win.jQuery = jQuery; //Publish method
})(window);

原型方法的优点是链接方法和属性非常容易。例如：

The advantage of the prototype method is that it's very easy to chain methods and properties. For example:

$("body").find("div:first").addClass("foo");

实现此功能的方法可能是：

A method to implement this feature could be:

$.fn.find = function(selector) {
    ...
    return $(...);
};

如果您对jQuery的实际实现感兴趣，请查看带注释的源代码：

If you're interested in jQuery's real implementation, have a look at the annotated source code:

• - 构造函数和基本方法的定义。


• jQuery.fn.extend 是用于。


• 。

• jQuery core - Definitions of the constructor and base methods.
• jQuery.fn.extend is used to add removeClass, etc. to jQuery.
• jQuery 1.7.1.

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