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JavaScript基于对象编程

1、JavaScript变量/函数声明在代码执行之前被解析，并且变量声明优先级高于函数声明。

代码片段：

var flag = 'test' in window;

if (!flag){

var test = 1;

}

new StringBuffer( 'test = ' ).append(test).toString();

执行结果：

test = undefined

2、JavaScript中的this关键字指向当前执行上下文对象。

代码片段：

var _this = this ;

var id;

var name;

function User(){

id = 110;

this .name = 'andy' ;

return this ;

}

var userOject = new User();

var _new_id = id;

var _new_name = name;

var _obj_id = userOject.id;

var _obj_name = userOject.name;

var userFunc = User();

var _id = id;

var _name = name;

var _func_id = userFunc.id;

var _func_name = userFunc.name;

new StringBuffer( '_this = ' ).append( _this ).

append( ';userOject = ' ).append(userOject ).append( ';_new_id = ' ).append(_new_id).append( ';_new_name = ' ).append(_new_name ).

append( ';_obj_id = ' ).append(_obj_id ).append( ';_obj_name = ' ).append( _obj_name ).

append( ';userFunc = ' ).append(userFunc ).append( ';_id = ' ).append(_id ).append( ';_name = ' ).append(_name).

append( ';_func_id = ' ).append(_func_id ).append( ';_func_name = ' ).append( _func_name).toString();

执行结果：

_this = [object Window]
userOject = [object Object]
_new_id = 110
_new_name = undefined
_obj_id = undefined
_obj_name = andy
userFunc = [object Window]
_id = 110
_name = andy
_func_id = 110
_func_name = andy

3、JavaScript中通过new关键字调用的函数才是构造函数。(在构造函数内部 - 也就是被调用的函数内 - this 指向新创建的对象 Object。)

代码片段：

function User(userName){

this .userName = userName;

return this ;

}

var zhengwei = User( '郑伟' );

var andy = new User( 'andy' );

new StringBuffer( 'zhengwei.constructor = ' ).append(zhengwei.constructor).

append( ';zhengwei instanceof User =' ).append((zhengwei instanceof User)).

append( ';andy.constructor = ' ).append(andy.constructor).

append( ';andy instanceof User = ' ).append((andy instanceof User)).toString();

执行结果：

zhengwei.constructor = [object Window]
zhengwei instanceof User =false
andy.constructor = function User(userName){this.userName = userNamereturn this}
andy instanceof User = true

4、JavaScript中所有变量都是对象，除了两个例外 null 和 undefined。

代码片段：

var undefind_test = 'undefind' in window;

var null_test = 'null' in window;

var _undefind = null ;

var undefind_toString;

try {

undefind_toString = undefind.toString();

} catch (e){

undefind_toString = e;

}

var null_toString;

try {

null_toString = null .toString();

} catch (e){

null_toString = e;

}

var boolean_toString = false .toString();

var number_toString = (2..toString() || 2 .toString() || (2).toString());

var array_toString = [1,2,3].toString();

new StringBuffer( 'undefind_test = ' ).append(undefind_test).

append( ';null_test = ' ).append( null_test).

append( ';_undefind = ' ).append(_undefind).

append( ';undefind_toString = ' ).append(undefind_toString).

append( ';null_toString = ' ).append(null_toString).

append( ';boolean_toString = ' ).append(boolean_toString).

append( ';number_toString = ' ).append(number_toString).

append( ';array_toString = ' ).append(array_toString).toString();

执行结果：

undefind_test = false
null_test = false
_undefind = null
undefind_toString = ReferenceError: undefind is not defined
null_toString = TypeError: null has no properties
boolean_toString = false
number_toString = 2
array_toString = 1,2,3

5、JavaScript的对象可以作为哈希表使用，主要用来保存命名的键与值的对应关系。使用对象的字面语法 - {} - 可以创建一个简单对象。这个新创建的对象从 Object.prototype 继承。

代码片段：

var Person = {id : '001' , userName : '郑伟' };

Person.age = 28;

new StringBuffer( "Person = " ).append(Person).

append( ";Person.constructor = " ).append(Person.constructor).

append( ";(Person instanceof Object) = " ).append((Person instanceof Object)).

append( ";Person['id'] = " ).append(Person[ 'id' ]).

append( ";Person.userName = " ).append(Person.userName).

append( ";Person['age'] = " ).append(Person[ 'age' ]).toString();

执行结果：

Person = [object Object]
Person.constructor = function Object() {[native code]
}
(Person instanceof Object) = true
Person['id'] = 001
Person.userName = 郑伟
Person['age'] = 28

6、JavaScript原型属性。(基于原型模型实现继承的对象最终形成原型链,新创建的对象的 prototype 被指向到构造函数的 prototype)

代码片段：

var Person = function (){};

Person.prototype = new Object();

// early binding -- Class template

Person.prototype.id = '001' ;

Person.prototype.userName = '郑伟' ;

Person.prototype.age = 28;

Person.prototype.say = function (){

return "[id = " + this .id + ", userName = " + this .userName + ",age = " + this .age + "]" ;

}

var person = new Person();

// later binding -- Instance template

/*person.id = '001'

person.userName = '郑伟';

person.age = 28;

person.say = function(){

return "[id = " + this.id + ", userName = " + this.userName + ",age = " + this.age + "]";

}*/

var _prototype_toString = new StringBuffer();

var count = -1;

for ( var n in Person.prototype) {

if (count >= 0){

_prototype_toString.append( "," );

}

_prototype_toString.append(n).append( "=" ).append(Person.prototype[n]);

count ++;

}

new StringBuffer( 'Object.prototype = ' ).append(Object.prototype).

append( ';Object.constructor = ' ).append(Object.constructor).

append( ';Object.prototype.constructor = ' ).append(Object.prototype.constructor).

append( ';(person instanceof Object) = ' ).append((Person instanceof Object)).

append( ';person.constructor = ' ).append(Person.constructor).

append( ";person.say() = " ).append(person.say()).

append( ";_prototype_toString = " ).append(_prototype_toString.toString()).toString();

执行结果：

Object.prototype = [object Object]
Object.constructor = function Function() {[native code]
}
Object.prototype.constructor = function Object() {[native code]
}
(person instanceof Object) = true
person.constructor = function Function() {[native code]
}
person.say() = [id = 001, userName = 郑伟,age = 28]
_prototype_toString = id=001,userName=郑伟,age=28,say=function (){return "[id = " + this.id + ", userName = " + this.userName + ",age = " + this.age + "]"}

7、基于构造函数（对象冒充）实现JavaScript对象继承。（支持多重继承，不支持instanceof关键字，多层继承时调用层次过多）

代码片段：

// Define baseClass.

function BaseClass(id, name){

this .id = id;

this .name = name;

this .toString = function (){

return 'id = ' + this .id + ', name =' + this .name;

};

}

// Define subclass.

function SubClass(){

BaseClass.apply( this , arguments);

this .identifer = arguments[arguments.length - 1];

this .toString = function (){

return BaseClass.prototype.toString.call( this ) + ', identifer = ' + this .identifer;

};

}

var subClass = new SubClass(1, 'subClass' , '0001' );

new StringBuffer( 'subClass.toString() = ' ).append(subClass.toString()).

append( ';subClass.constructor = ' ).append(subClass.constructor).

append( ';(subClass.constructor === SubClass) = ' ).append((subClass.constructor === SubClass)).

append( ';(subClass instanceof SubClass) = ' ).append((subClass instanceof SubClass)).

append( ';(subClass instanceof BaseClass) = ' ).append((subClass instanceof BaseClass)).toString();

执行结果：

subClass.toString() = [object Object], identifer = 0001
subClass.constructor = function SubClass(){BaseClass.apply(this, arguments)this.identifer = arguments[arguments.length - 1]this.toString = function(){return BaseClass.prototype.toString.call(this) + ', identifer = ' + this.identifer}}
(subClass.constructor  === SubClass) = true
(subClass instanceof SubClass) = true
(subClass instanceof BaseClass) = false

8、基于原型（代码模板）实现JavaScript对象继承。（不支持多重继承，支持instanceof关键字，多层继承时模版复用）

代码片段：

// Define baseClass

function BaseClass(){}

BaseClass.prototype.id = null ;

BaseClass.prototype.name = null ;

BaseClass.prototype.toString = function (){

return 'id = ' + this .id + ', name =' + this .name;

};

// Define subClass

function SubClass(){}

SubClass.prototype = new BaseClass();

SubClass.prototype.identifer = null ;

SubClass.prototype.toString = function (){

return BaseClass.prototype.toString.call( this ) + ', identifer = ' + this .identifer;

};

// The subclass is instanced.

var subClass = new SubClass();

subClass.id = 1;

subClass.name = 'subClass' ;

subClass.identifer = '0001' ;

// Output

new StringBuffer( 'subClass.toString() = ' ).append(subClass.toString()).

append( ';subClass.constructor = ' ).append(subClass.constructor).

append( ';(subClass.constructor === SubClass) =' ).append((subClass.constructor === SubClass)).

append( ';(subClass instanceof SubClass) = ' ).append((subClass instanceof SubClass)).

append( ';(subClass instanceof BaseClass) = ' ).append((subClass instanceof BaseClass)).toString();

执行结果：

subClass.toString() = id = 1, name =subClass, identifer = 0001
subClass.constructor = function BaseClass(){}
(subClass.constructor  === SubClass) =false
(subClass instanceof SubClass) = true
(subClass instanceof BaseClass) = true

9、基于构造函数（封装类属性-成员变量） + 原型（封装类行为-方法）实现JavaScript对象继承。（不支持多重继承，支持instanceof关键字，多层继承时模版复用）

代码片段：

// Define baseclass.

function BaseClass(id, name){

this .id = id;

this .name = name;

}

// Overwrite toString method.

BaseClass.prototype.toString = function (){

return 'id = ' + this .id + ', name =' + this .name;

};

// Define subclass.

function SubClass(){

BaseClass.apply( this , arguments);

this .identifer = arguments[arguments.length - 1];

}

// Subclass extends base class.

SubClass.prototype = new BaseClass();

SubClass.prototype.constructor = SubClass;

SubClass.prototype.toString = function (){

return BaseClass.prototype.toString.call( this ) + ', identifer = ' + this .identifer;

};

// The subclass is intanced.

var subClass = new SubClass(1, 'subClass' , '0001' );

// Output

new StringBuffer( 'subClass.toString() = ' ).append(subClass.toString()).

append( ';subClass.constructor = ' ).append(subClass.constructor).

append( ';(subClass.constructor === SubClass) =' ).append((subClass.constructor === SubClass)).

append( ';(subClass instanceof SubClass) = ' ).append((subClass instanceof SubClass)).

append( ';(subClass instanceof BaseClass) = ' ).append((subClass instanceof BaseClass)).toString();

执行结果：

subClass.toString() = id = 1, name =subClass, identifer = 0001
subClass.constructor = function SubClass(){BaseClass.apply(this, arguments)this.identifer = arguments[arguments.length - 1]}
(subClass.constructor  === SubClass) =true
(subClass instanceof SubClass) = true
(subClass instanceof BaseClass) = true

10、基于对象结构（哈希表key-value）实现JavaScript对象继承。（支持多重继承，不支持instanceof关键字，多层继承时模版迭代）

代码片段：

// Define class factory.

var ClassFactory = {

createClass : function (){

// To defind the current constructor.

var CurrentClass = function (){};

// Agreed the final parameter for the current class extends the prototype, for the rest of the parameters so as to realize the parent class.

var extendsPrototype = arguments[arguments.length - 1] || {};

for ( var i in arguments){

if (i == arguments.length - 1) break ;

var superClass = arguments[i];

var ordinal = superClass.ORDINAL = i;

if ( 'function' === typeof (superClass)){

superClass = superClass.prototype;

}

var superPrototype = extendsPrototype[ordinal] = {};

for ( var key in superClass) {

// Determine whether the current members of the current class

if (superClass.hasOwnProperty(key)){

superPrototype[key] = superClass[key];

} else {

extendsPrototype[key] = superClass[key];

}

// Prototype will expand after the prototype chain of pointing to the current class.

CurrentClass.prototype = extendsPrototype;

CurrentClass.prototype.constructor = CurrentClass;

return CurrentClass;

}

};

// Define class A

var A = ClassFactory.createClass({

width : 100,

getWidth : function (){

return this .width;

}

});

// Define class B

var B = ClassFactory.createClass({

width : 200,

height : 100,

getWidth : function (){

return this .width;

getHeight : function (){

return this .height;

}

});

// Define class C

var C = ClassFactory.createClass(A, B,{

width : 300,

getWidth : function (){

return this .width;

}

});

// Initialize C object

var c = new C();

// Output

new StringBuffer( 'c.constructor = ' ).append(c.constructor).

append( ';(c.constructor === C) = ' ).append((c.constructor === C)).

append( ';(c instanceof C) = ' ).append((c instanceof C)).

append( ';((c instanceof A) || (c instanceof B)) = ' ).append(((c instanceof A) || (c instanceof B))).

append( ';c.getWidth() = ' ).append(c.getWidth()).

append( ';c[A.ORDINAL].getWidth() = ' ).append( (c[A.ORDINAL]).getWidth() ).

append( ';c[B.ORDINAL].getWidth() = ' ).append( (c[B.ORDINAL]).getWidth() ).

append( ';c[B.ORDINAL].getHeight() = ' ).append( (c[B.ORDINAL]).getHeight() ).toString();

执行结果：

c.constructor = function (){}
(c.constructor === C) = true
(c instanceof C) = true
((c instanceof A) || (c instanceof B)) = false
c.getWidth() = 300
c[A.ORDINAL].getWidth() = 100
c[B.ORDINAL].getWidth() = 200
c[B.ORDINAL].getHeight() = 100

11、基于构造函数（封装类属性-成员变量） + 原型（封装类行为-方法）实现JavaScript对象继承推荐写法。（不支持多重继承，支持instanceof关键字，多层继承时模版复用）

代码片段：

// Define class factory.

var ClassFactory = {

createClass : function (){

// To defind the current constructor.

// TODO set member Variables

var CurrentClass = function (){

if ( this .initialize){

this .initialize.apply( this , arguments);

}

};

// The current class to extends base class.

var SuperClass = arguments[0] || '' ;

if ( typeof (SuperClass) === 'function' ){

CurrentClass.prototype = new SuperClass();

} else {

// If current class is base class, then current class prototype direct at Object prototype.

CurrentClass.prototype = new Object();

}

CurrentClass.prototype.constructor = CurrentClass;

// The current class to extend prototype.

var extendsPrototype = arguments[arguments.length - 1] || {};

for ( var key in extendsPrototype){

CurrentClass.prototype[key] = extendsPrototype[key];

}

return CurrentClass;

}

// Define base class.

var SuperComponent = ClassFactory.createClass({

initialize : function (title, index){

this .rootNodeName = 'js_oo' ;

this .className = 'demo_container' ;

this .title = title;

this .index = index;

getScript : function (){

throw new Error( 'The method must be implemented sub class!' );

}

});

// Define sub class.

var TestComponent = ClassFactory.createClass(SuperComponent, {

getScript : function (){

var _script = new StringBuffer();

_script.append( this .title);

return _script.toString();

}

});

var testComponent = new TestComponent( "TestComponent" , 2);

// Output

new StringBuffer( 'testComponent.constructor = ' ).append(testComponent.constructor).

append( ';(testComponent.constructor === TestComponent) = ' ).append((testComponent.constructor === TestComponent)).

append( ';(testComponent instanceof TestComponent) = ' ).append((testComponent instanceof TestComponent)).

append( ';(testComponent instanceof SuperComponent) = ' ).append((testComponent instanceof SuperComponent)).

append( ';testComponent.getScript() = ' ).append(testComponent.getScript()).toString();

执行结果：

testComponent.constructor = function (){if(this.initialize){this.initialize.apply(this, arguments)}}
(testComponent.constructor === TestComponent) = true
(testComponent instanceof  TestComponent) = true
(testComponent instanceof  SuperComponent) = true
testComponent.getScript() = TestComponent

转载于:https://my.oschina.net/andy0807/blog/190677