JavaScript继承的一些工具函数

在阅读精通JavaScript(图灵计算机科学丛书)里面有讲解javascript继承的一些东东。

其一是讲解DouglasCrockford的js

代码如下：

//简单的辅助函数，让你可以将新函数绑定到对象prototype上
Function.prototype.method = function (name, func) {
this.prototype[name] = func;
return this;
}
//一个相当复杂的函数，允许你方便地从其他对象继承函数，
//同时仍然可以调用属于父对象的那些方法
Function.method('inherits', function (parent) {
var d = {}; //记录我们目前所在父层次的级数
var p = (this.prototype = new parent()); //继承父对象的方法
//创建一个新的名位uber的特权函数
//调用它时会执行所有在继承时被重写的函数
this.method("uber", function uber(name) {
if (!(name in d)) {
d[name] = 0; //继承级数默认为0
}
var f, /*要执行的函数*/r, /*函数返回值*/t = d[name], v = parent.prototype; /*父对象的prototype*/
if (t) {
//如果我们已经在某个uber函数内 上溯到必要的级数已找到原始的prototype
while (t) {
v = v.constructor.prototype;
t -= 1;
}
f = v[name]; //从prototype中获得函数
}
else {
//uber第一次调用 从prototype获得要执行的函数
f = p[name];
if (f == this[name]) {
//如果函数属于当前prototype 则改为调用父对象的prototype
f = v[name];
}
}
d[name] += 1; //记录我们在继承堆栈中所在位置
//使用除第一个以外所有的arguments 调用函数 第一个参数是执行的匿名函数名
r = f.apply(this, Array.prototype.slice.apply(arguments, [1]));
d[name] -= 1; //恢复继承堆栈
return r;
});
return this;
});
//只继承父对象特定的函数。而非使用new parent（）的继承的所有函数
Function.method("swiss", function (parent) {
for (var i = 1; i < arguments.length; i++) {
var name = arguments[i];
this.prototype[name] = parent[name];
}
return this;
});
/* Function.prototype.method 它提供了一个简单的方法，把函数于构造函数原型关联起来。
之所以有效，是因为所有的构造函数本身都是函数，所以能获得method这个新方法
Function.prototype.inherits这一函数可以用于提供简单的对象继承，它的代码主要围绕任意对象方法中调用
this.uber（methodname）为中心，并在让这个uber方法执行它要覆盖的父对象的方法。
Function.prototype.swiss这是.method函数的增强版，可以用于单一父对象获取多个函数。如果有多个父对象上
就能获得可用的多对象继承
*/

调用代码：

function Person(name) {
this.name = name;
}
Person.method("getName", function () { return this.name; });
function User(name, password) {
this.name = name;
this.password = password;
}
User.inherits(Person);
User.method("getPassword", function () { return this.password; });
User.method("getName", function () { return "My name is :" + this.uber("getName"); });

var p = new Person("123");
alert(p.getName());
var u = new User("abc", "456");
alert(u.getPassword());
alert(u.getName());

第二个工具函数是base库

代码：

/*
Base.js, version 1.1a
Copyright 2006-2010, Dean Edwards
License: http://www.opensource.org/licenses/mit-license.php */

var Base = function() {
// dummy
};

Base.extend = function(_instance, _static) { // subclass
var extend = Base.prototype.extend;

// build the prototype
Base._prototyping = true;
var proto = new this;
extend.call(proto, _instance);
proto.base = function() {
// call this method from any other method to invoke that method's ancestor
};
delete Base._prototyping;

// create the wrapper for the constructor function
//var constructor = proto.constructor.valueOf(); //-dean
var constructor = proto.constructor;
var klass = proto.constructor = function() {
if (!Base._prototyping) {
if (this._constructing || this.constructor == klass) { // instantiation
this._constructing = true;
constructor.apply(this, arguments);
delete this._constructing;
} else if (arguments[0] != null) { // casting
return (arguments[0].extend || extend).call(arguments[0], proto);
}
}
};

// build the class interface
klass.ancestor = this;
klass.extend = this.extend;
klass.forEach = this.forEach;
klass.implement = this.implement;
klass.prototype = proto;
klass.toString = this.toString;
klass.valueOf = function(type) {
//return (type == "object") ? klass : constructor; //-dean
return (type == "object") ? klass : constructor.valueOf();
};
extend.call(klass, _static);
// class initialisation
if (typeof klass.init == "function") klass.init();
return klass;
};

Base.prototype = {
extend: function(source, value) {
if (arguments.length > 1) { // extending with a name/value pair
var ancestor = this[source];
if (ancestor && (typeof value == "function") && // overriding a method?
// the valueOf() comparison is to avoid circular references
(!ancestor.valueOf || ancestor.valueOf() != value.valueOf()) &&
/\bbase\b/.test(value)) {
// get the underlying method
var method = value.valueOf();
// override
value = function() {
var previous = this.base || Base.prototype.base;
this.base = ancestor;
var returnValue = method.apply(this, arguments);
this.base = previous;
return returnValue;
};
// point to the underlying method
value.valueOf = function(type) {
return (type == "object") ? value : method;
};
value.toString = Base.toString;
}
this[source] = value;
} else if (source) { // extending with an object literal
var extend = Base.prototype.extend;
// if this object has a customised extend method then use it
if (!Base._prototyping && typeof this != "function") {
extend = this.extend || extend;
}
var proto = {toSource: null};
// do the "toString" and other methods manually
var hidden = ["constructor", "toString", "valueOf"];
// if we are prototyping then include the constructor
var i = Base._prototyping ? 0 : 1;
while (key = hidden[i++]) {
if (source[key] != proto[key]) {
extend.call(this, key, source[key]);

}
}
// copy each of the source object's properties to this object
for (var key in source) {
if (!proto[key]) extend.call(this, key, source[key]);
}
}
return this;
}
};

// initialise
Base = Base.extend({
constructor: function() {
this.extend(arguments[0]);
}
}, {
ancestor: Object,
version: "1.1",

forEach: function(object, block, context) {
for (var key in object) {
if (this.prototype[key] === undefined) {
block.call(context, object[key], key, object);
}
}
},

implement: function() {
for (var i = 0; i < arguments.length; i++) {
if (typeof arguments[i] == "function") {
// if it's a function, call it
arguments[i](this.prototype);
} else {
// add the interface using the extend method
this.prototype.extend(arguments[i]);
}
}
return this;
},

toString: function() {
return String(this.valueOf());
}
});


调用代码：
var Person = Base.extend({
constructor: function (name) { this.name = name; },
getName: function () { return this.name; }
});

var User = Person.extend({
constructor: function (name, password) {
this.base(name);
this.password = password;
},
getPassWord: function () { return this.password; }
});

var p = new Person("123");
alert(p.getName());
var u = new User("456", "abc");
alert(u.getName());
alert(u.getPassWord());

有关base的详细介绍：http://dean.edwards.name/weblog/2006/03/base/