1、面向对象的工厂方法
var person2 = createPerson("Greg",27,"Doctor");
person1.sayName(); //"Nicholas"
person2.sayName(); //"Greg"
2、构造函数模式创建对象
var person2 = new Person("Greg","Doctor");
person1.sayName(); //"Nicholas"
person2.sayName(); //"Greg"
alert(person1 instanceof Object); //true
alert(person1 instanceof Person); //true
alert(person2 instanceof Object); //true
alert(person2 instanceof Person); //true
alert(person1.constructor == Person); //true
alert(person2.constructor == Person); //true
alert(person1.sayName == person2.sayName); //false
使用new关键字创建对象会经历以下四个过程
3、将构造函数当函数用
person.sayName(); //"Nicholas"
Person("Greg","Doctor"); //adds to window
window.sayName(); //"Greg"
var o = new Object();
Person.call(o,"Kristen",25,"Nurse");
o.sayName(); //"Kristen"
构造函数当做函数使用就和普通的函数没有任何不同,它属于window对象下面添加的方法而已。由于构造函数创建的对象实际上是创建一个新对象,因此在本质上两者还是不一样的,还是分离的,他们的方法还是不一样的!
4、将共有的方法方法全局解决不一致的问题
alert(this.name);
}
var person1 = new Person("Nicholas","Doctor");
person1.sayName(); //"Nicholas"
person2.sayName(); //"Greg"
alert(person1 instanceof Object); //true
alert(person1 instanceof Person); //true
alert(person2 instanceof Object); //true
alert(person2 instanceof Person); //true
alert(person1.constructor == Person); //true
alert(person2.constructor == Person); //true
alert(person1.sayName == person2.sayName); //true
虽然上面的方法解决了一致的问题,但是定义的全局的方法本身属于window,那么局部和全局就没有分开!所以这个方法使用的并不多见!也不建议使用。
5、原型模式
我们创建的任何的一个函数都有一个原型对象,这个属性是一个指针,它指向一个对象,而这个对象的作用是可以有特定的类型的所有的实例共享的方法!
Person.prototype.age = 29;
Person.prototype.job = "Software Engineer";
Person.prototype.sayName = function(){
alert(this.name);
};
var person1 = new Person();
person1.sayName(); //"Nicholas"
var person2 = new Person();
person2.sayName(); //"Nicholas"
alert(person1.sayName == person2.sayName); //true
alert(Person.prototype.isPrototypeOf(person1)); //true
alert(Person.prototype.isPrototypeOf(person2)); //true
//only works if Object.getPrototypeOf() is available
if (Object.getPrototypeOf){
alert(Object.getPrototypeOf(person1) == Person.prototype); //true
alert(Object.getPrototypeOf(person1).name); //"Nicholas"
}
无论什么时候只要是创建了一个函数,就会创建一个原型属性,这个属性指向函数的原型对象。在默认的情况下,原型对象都会包含一个constructor(构造函数属性),这个属性包含一个指向prototype属性所在函数的指针!
属性读取的顺序
每当代码读取某个对象的属性时候,都会执行一次搜索,目标是具有给定名字的属性,搜索从对象的实例本身开始查找,如有则返回,没有则继续搜索该对象的原型链,直至搜索到原型链的最外层!
Person.prototype.age = 29;
Person.prototype.job = "Software Engineer";
Person.prototype.sayName = function(){
alert(this.name);
};
var person1 = new Person();
var person2 = new Person();
person1.name = "Greg";
alert(person1.name); //"Greg" 来自实例
alert(person2.name); //"Nicholas" 来自原型
Person.prototype.age = 29;
Person.prototype.job = "Software Engineer";
Person.prototype.sayName = function(){
alert(this.name);
};
var person1 = new Person();
var person2 = new Person();
person1.name = "Greg";
alert(person1.name); //"Greg" ?from instance
alert(person2.name); //"Nicholas" ?from prototype
delete person1.name;
alert(person1.name); //"Nicholas" - from the prototype
6、hasOwnProperty方法
这个方法可以检测一个属性是否存在于实例中,还是存在于原型中!hasOwnProperty是从Object继承来的,只要给定属性存在于对象实例中,才会返回true.
Person.prototype.name = "Nicholas";
Person.prototype.age = 29;
Person.prototype.job = "Software Engineer";
Person.prototype.sayName = function(){
alert(this.name);
};
var person1 = new Person();
var person2 = new Person();
alert(person1.hasOwnProperty("name")); //false
alert("name" in person1); //true
person1.name = "Greg";
alert(person1.name); //"Greg" ?from instance
alert(person1.hasOwnProperty("name")); //true
alert("name" in person1); //true
alert(person2.name); //"Nicholas" ?from prototype
alert(person2.hasOwnProperty("name")); //false
alert("name" in person2); //true
delete person1.name;
alert(person1.name); //"Nicholas" - from the prototype
alert(person1.hasOwnProperty("name")); //false
alert("name" in person1); //true
7、Object.keys() 可枚举属性方法
这个方法接收一个对象作为参数,返回一个包含所有可枚举属性的字符串数组
Person.prototype.name = "Nicholas";
Person.prototype.age = 29;
Person.prototype.job = "Software Engineer";
Person.prototype.sayName = function(){
alert(this.name);
};
var keys = Object.keys(Person.prototype);
alert(keys); //"name,job,sayName"
如果想得到所有实例的属性,无论它是否可以枚举都可以使用这个方法来获取
function Person(){
}
Person.prototype.name = "Nicholas";
Person.prototype.age = 29;
Person.prototype.job = "Software Engineer";
Person.prototype.sayName = function(){
alert(this.name);
};
var keys = Object.getOwnPropertyNames(Person.prototype);
alert(keys); //"constructor,name,sayName"
8、简单的原型写法
Person.prototype = {
name : "Nicholas",age : 29,job: "Software Engineer",sayName : function () {
alert(this.name);
}
};
var friend = new Person();
alert(friend instanceof Object); //true
alert(friend instanceof Person); //true
alert(friend.constructor == Person); //false
alert(friend.constructor == Object); //true
重写了原型就等于将默认的原型方法覆盖,那么同样的构造方法也会被重写,重写的构造方法指向了Object对象!而不是原来的对象Person
Person.prototype = {
constructor : Person,name : "Nicholas",sayName : function () {
alert(this.name);
}
};
var friend = new Person();
alert(friend instanceof Object); //true
alert(friend instanceof Person); //true
alert(friend.constructor == Person); //true
alert(friend.constructor == Object); //false
9、原型方法的动态添加
Person.prototype = {
constructor: Person,job : "Software Engineer",sayName : function () {
alert(this.name);
}
};
var friend = new Person();
Person.prototype.sayHi = function(){
alert("hi");
};
friend.sayHi(); //"hi" ?works!
10、原生对象的原型方法
String.prototype.startsWith = function (text) {//<a href="/tag/xiugai/" target="_blank" class="keywords">修改</a>原生对象的原型<a href="/tag/fangfa/" target="_blank" class="keywords">方法</a>
return this.indexOf(text) == 0;
};
var msg = "Hello world!";
alert(msg.startsWith("Hello")); //true
11、组合使用构造函数和原型模式创建对象
var person1 = new Person("Nicholas","Software Engineer");
var person2 = new Person("Greg","Doctor");
person1.friends.push("Van");
alert(person1.friends); //"Shelby,Court,Van"
alert(person2.friends); //"Shelby,Court"
alert(person1.friends === person2.friends); //false
alert(person1.sayName === person2.sayName); //true
12、动态原型模式
//properties
this.name = name;
this.age = age;
this.job = job;
//methods
if (typeof this.sayName != "function"){
Person.prototype.sayName = function(){
alert(this.name);
};
}
}
var friend = new Person("Nicholas","Software Engineer");
friend.sayName();
13、寄生构造函数模式
friend.sayName(); //"Nicholas"
function SpecialArray(){
//create the array
var values = new Array();
//add the values
values.push.apply(values,arguments);
//assign the method
values.toPipedString = function(){
return this.join("|");
};
//return it
return values;
}
var colors = new SpecialArray("red","blue","green");
alert(colors.toPipedString()); //"red|blue|green"
alert(colors instanceof SpecialArray);
上诉方法有一点说明下,由于它是依赖外层对象来创建一个新对象,因此不能依赖 instanceof方法来确定属性和方法的来源!它实际上和构造函数的没有关系!
14、稳妥构造函数模式
var friend = Person("Nicholas","Software Engineer");
friend.sayName(); //"Nicholas"
此方法不依赖任何new this 关键符!如果要访问对象的方法和属性,只能通过对象已经定义好的方法来获取!
15、继承
javascript实现继承是通过原型链来实现的SuperType.prototype.getSuperValue = function(){//定义的原型<a href="/tag/fangfa/" target="_blank" class="keywords">方法</a>
return this.property;
};
function SubType(){
this.subproperty = false;
}
//inherit from SuperType
SubType.prototype = new SuperType();
SubType.prototype.getSubValue = function (){
return this.subproperty;
};
var instance = new SubType();
alert(instance.getSuperValue()); //true
alert(instance instanceof Object); //true
alert(instance instanceof SuperType); //true
alert(instance instanceof SubType); //true
alert(Object.prototype.isPrototypeOf(instance)); //true
alert(SuperType.prototype.isPrototypeOf(instance)); //true
alert(SubType.prototype.isPrototypeOf(instance)); //true
SubType继承SuperType的方法和属性,因此当instance可以直接调用SuperType的方法!
function SuperType(){
this.property = true;
}
SuperType.prototype.getSuperValue = function(){
return this.property;
};
function SubType(){
this.subproperty = false;
}
//inherit from SuperType
SubType.prototype = new SuperType();
//new method
SubType.prototype.getSubValue = function (){
return this.subproperty;
};
//override existing method
SubType.prototype.getSuperValue = function (){
return false;
};
var instance = new SubType();
alert(instance.getSuperValue()); //false
上面的例子说明,重写的原型会覆盖之前继承的原型,最后返回的往往不是预期的效果
SuperType.prototype.getSuperValue = function(){
return this.property;
};
function SubType(){
this.subproperty = false;
}
//inherit from SuperType
SubType.prototype = new SuperType();
//使用字面量<a href="/tag/tianjia/" target="_blank" class="keywords">添加</a>的<a href="/tag/fangfa/" target="_blank" class="keywords">方法</a>导致上面的<a href="/tag/fangfa/" target="_blank" class="keywords">方法</a>失效了
SubType.prototype = {
getSubValue : function (){
return this.subproperty;
},someOtherMethod : function (){
return false;
}
};
var instance = new SubType();
console.log(instance);
alert(instance.getSuperValue()); //error!
下面的例子也说明重写原型带来的风险
function SubType(){
}
//inherit from SuperType
SubType.prototype = new SuperType();
var instance1 = new SubType();
instance1.colors.push("black");
alert(instance1.colors); //"red,blue,green,black"
var instance2 = new SubType();
alert(instance2.colors); //"red,black"
原型共享导致两个不同的对象调用的同一个数据
16、借用构造函数来实现继承
function SubType(){
//inherit from SuperType
SuperType.call(this);
}
var instance1 = new SubType();
instance1.colors.push("black");
alert(instance1.colors); //"red,green"
传递参数
function SubType(){
//inherit from SuperType passing in an argument
SuperType.call(this,"Nicholas");
//instance property
this.age = 29;
}
var instance = new SubType();
alert(instance.name); //"Nicholas";
alert(instance.age); //29
17、组合继承方式
SuperType.prototype.sayName = function(){
alert(this.name);
};
function SubType(name,age){
SuperType.call(this,name);
this.age = age;
}
18、原型继承
var person = {
name: "Nicholas",friends: ["Shelby","Court","Van"]
};
var anotherPerson = object(person);
anotherPerson.name = "Greg";
anotherPerson.friends.push("Rob");
19、寄生组合式继承
function inheritPrototype(subType,superType){
var prototype = object(superType.prototype); //create object
prototype.constructor = subType; //augment object
subType.prototype = prototype; //assign object
}
function SuperType(name){
this.name = name;
this.colors = ["red",name);
this.age = age;
}
inheritPrototype(SubType,SuperType);
SubType.prototype.sayAge = function(){
alert(this.age);
};
var instance1 = new SubType("Nicholas",29);
instance1.colors.push("black");
alert(instance1.colors); //"red,black"
instance1.sayName(); //"Nicholas";
instance1.sayAge(); //29
var instance2 = new SubType("Greg",27);
alert(instance2.colors); //"red,green"
instance2.sayName(); //"Greg";
instance2.sayAge(); //27
以上就是今天的javascript学习小结,之后每天还会继续更新,希望大家继续关注。