[原]JavaScript必备知识系列-继承的实现方式

JavaScript实现继承的几种方式

开发中常见的几种JavaScript继承方式，了解每一种都会有提高的，直接贴代码吧，更直接。

具体的JavaScript面向对象的概念理解参见JavaScript必备知识系列-面向对象知识串结

JavaScript必备知识系列，总目录参见JavaScript必备知识系列-开篇

拷贝继承

extend(obj) {
var args = Array.prototype.slice.call(arguments, 1);
args.forEach(function(source) {
for(var prop in source) {
obj[prop] = source[prop];
}
});
return obj;
}

forEach方法参见JavaScript必备知识系列-Array

原型链继承（YUI）

YAHOO.extend = function(subclass, superclass) {
var f = function() {};
f.prototype = superclass.prototype;
subclass.prototype = new f();
subclass.prototype.constructor = subclass;
subclass.superclass = superclass.prototype;
if (superclass.prototype.constructor == Object.prototype.constructor) {
superclass.prototype.constructor = superclass;
}
};

拷贝+原型链继承（Backbone）

// Shared empty constructor function to aid in prototype-chain creation.
var ctor = function(){};

// Helper function to correctly set up the prototype chain, for subclasses.
// Similar to `goog.inherits`, but uses a hash of prototype properties and
// class properties to be extended.
//parent是View、Model或Collection，protoProps为自定义属性，staticProps默认静态属性
var inherits = function(parent, protoProps, staticProps) {
var child;

// The constructor function for the new subclass is either defined by you
// (the "constructor" property in your `extend` definition), or defaulted
// by us to simply call the parent's constructor.
if (protoProps && protoProps.hasOwnProperty('constructor')) {
child = protoProps.constructor;
} else {
child = function(){ parent.apply(this, arguments); }; //child本身定义为一个function
}

// Inherit class (static) properties from parent.
_.extend(child, parent);

// Set the prototype chain to inherit from `parent`, without calling
// `parent`'s constructor function.
ctor.prototype = parent.prototype; //ctor是一个空的构造函数
child.prototype = new ctor();//child原型继承parent的原型

// Add prototype properties (instance properties) to the subclass,
// if supplied.
if (protoProps) _.extend(child.prototype, protoProps); //拷贝自定义属性给child的原型上

// Add static properties to the constructor function, if supplied.
if (staticProps) _.extend(child, staticProps);

// Correctly set child's `prototype.constructor`.
child.prototype.constructor = child;

// Set a convenience property in case the parent's prototype is needed later.
child.__super__ = parent.prototype;

return child; //此时的child是一个功能强大的方法了，还是一个function
};