原型在jQuery源代码中意味着什么? [英] What does prototype mean here in the jQuery source code?

问题描述

例如，从jQuery 1.2.6复制而来:

As an example, copied from jQuery 1.2.6:

jQuery.fn = jQuery.prototype = {
    init: function( selector, context ) {
        // Make sure that a selection was provided
        selector = selector || document;
        ..........
    },
};

我在这里阅读了一些帖子，例如> JavaScript:什么是.extend和.prototype用于?，并且知道可以在子类中使用原型来扩展某些方法.

I have read some posts here like JavaScript: What are .extend and .prototype used for? and know a prototype can be used in a subclass to extend some methods.

但是我无法理解上述jQuery片段中的用法.

But I cannot understand the usage in the above snippet from jQuery.

是否有描述原型的规范文档?

Are there any canonical documents describing the prototype?

谢谢.

推荐答案

所有对象都具有prototype属性.它只是一个对象，其他对象可以从中继承属性.您发布的代码片段只是将具有某些属性(例如init)的对象分配给jQuery的prototype，并将别名jQuery.prototype分配给jQuery.fn，因为fn较短且键入更快.如果您暂时忘记了jQuery，请考虑以下简单示例:

All objects have a prototype property. It is simply an object from which other objects can inherit properties. The snippet you have posted simply assigns an object with some properties (such as init) to the prototype of jQuery, and aliases jQuery.prototype to jQuery.fn because fn is shorter and quicker to type. If you forget about jQuery temporarily, consider this simple example:

function Person(name) {
    this.name = name;
}
Person.prototype.sayHello = function () {
    alert(this.name + " says hello");
};

var james = new Person("James");
james.sayHello(); // Alerts "James says hello"

在此示例中，Person是构造函数函数.可以通过new运算符对其进行实例化.在构造函数内部，this关键字引用实例，因此每个实例都有自己的name属性.

In this example, Person is a constructor function. It can be instantiated by calling it with the new operator. Inside the constructor, the this keyword refers to the instance, so every instance has its own name property.

Person的prototype在所有实例之间共享.因此，所有Person实例都有一个sayHello方法，它们从Person.prototype继承 .通过将sayHello方法定义为Person.prototype的属性，我们可以节省内存.我们可以很容易地给Person的每个实例自己的方法副本(通过将其分配给构造函数中的this.sayHello)，但是效率不高.

The prototype of Person is shared between all instances. So all instances of Person have a sayHello method that they inherit from Person.prototype. By defining the sayHello method as a property of Person.prototype we are saving memory. We could just as easily give every instance of Person its own copy of the method (by assigning it to this.sayHello inside the constructor), but that's not as efficient.

在jQuery中，当您调用$方法时，您实际上是在创建jQuery.prototype.init的实例(记住jQuery.fn === jQuery.prototype):

In jQuery, when you call the $ method, you're really creating an instance of jQuery.prototype.init (remember that jQuery.fn === jQuery.prototype):

return new jQuery.fn.init(selector, context, rootjQuery);

如果您查看jQuery.fn.init:

jQuery.fn.init.prototype = jQuery.fn;

实际上，您正在创建jQuery的实例，该实例可以访问在jQuery.prototype上声明的所有方法.如前所述，这比在jQuery的每个实例上声明这些方法要有效得多.

So really, you're creating an instance of jQuery which has access to all the methods declared on jQuery.prototype. As discussed previously, this is much more efficient than declaring those methods on each instance of jQuery.

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