(I) Constructor
Create a constructor, designed to create a Person object
The constructor is an ordinary function, and the way to create a normal function is no different,
The difference is that the constructor's first letter capitalized habit
Constructors and normal function of the difference is the way of calling
Normal function is called directly , while the constructor need to use the new keyword to call
Example: create a constructor
function Person(){
alert(this);
}
was a = new Person ();
console.log(per);
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(Ii) the execution flow constructor
1. Create a new object immediately
2. The new object is set to this function, may be used in this new constructor to refer to objects
3. The function of the code line by line
4. The new object is returned as the return value
Specific examples are as follows:
function Person(name , age , gender){
this.name = name;
this.age = age;
this.gender = gender;
this.sayName = function(){
alert(this.name);
}；
}
var per = new new the Person ( " Monkey " , 18 , " M " );
var Per2 = new new the Person ( " rabbit fine " , 16 , " F " );
var Per3 = new new the Person ( " rush Pa " , 38 , " M " );
console.log(per);
console.log(per2);
console.log(per3);
The results are shown below:
(Iii) the class and instance of the class
Use objects created with a constructor, we called a class of objects, also known as a constructor of a class.
We will create an object constructor, called an instance of the class
Specific example: re-create the function of a Dog
function Person(name , age , gender){
this.name = name;
this.age = age;
this.gender = gender;
this.sayName = function(){
alert(this.name);
}；
}
function Dog(){
}
var per = new Person("孙悟空",18,"男");
var per2 = new Person("玉兔精",16,"女");
var per3 = new Person("奔波霸",38,"男");
var dog = new Dog();
console.log(per);
console.log(dog);
显示结果为：
㈣ instanceof
使用 instanceof 可以检查一个对象是否是一个类的实例
语法：对象 instanceof 构造函数
如果是，返回true，否则返回false
具体示例：
function Person(name , age , gender){
this.name = name;
this.age = age;
this.gender = gender;
this.sayName = function(){
alert(this.name);
}；
}
function Dog(){
}
var per = new Person("孙悟空",18,"男");
var per2 = new Person("玉兔精",16,"女");
var per3 = new Person("奔波霸",38,"男");
var dog = new Dog();
①console.log(per instanceof Person);
②console.log(dog instanceof Person);
③console.log(dog instanceof Object);
第一个结果是：true
第二个结果是：false
第三个结果是：true
注意：所有的对象都是Object的后代，所以任何对象和Object做instanceof检查时都会返回true
㈤代码优化—将sayName方法在全局作用域中定义
创建一个Person构造函数
在Person构造函数中，为每一个对象都添加了一个sayName方法，目前我们的方法是在构造函数内部创建的
也就是构造函数每执行一次就会创建一个新的sayName方法，也就是所有实例的sayName都是唯一的。
这样就导致了构造函数执行一次就会创建一个新的方法，
执行10000次就会创建10000个新的方法，而10000个方法都是一模一样的
这是没有必要的，完全可以使所有的对象共享同一个方法
具体示例如下：
function PersonOne(name , age , gender){
this.name = name;
this.age = age;
this.gender = gender;
//向对象中添加一个方法
this.sayName = fun;
}
//将sayName方法在全局作用域中定义
function fun(){
alert("Hello大家好，我是："+this.name);
};
//创建一个Person的实例
var per = new PersonOne("孙悟空",18,"男");
var per2 = new PersonOne("猪八戒",28,"男");
per.sayName();
per2.sayName();
console.log(per.sayName == per2.sayName);
结果为：true
注意：这种方法有一定的问题：将函数定义在全局作用域，污染了全局作用域的命名空间，而且定义在在全局作用域中也很不安全
㈥代码优化2—原型中添加sayName方法
上面的代码该如何继续优化呢？那么可以怎么改呢？向原型中添加sayName方法
以后我们创建构造函数时，可以将这些对象共有的属性和方法，统一添加到构造函数的原型对象中，
这样不用分别为每一个对象添加，也不会影响到全局作用域，就可以使每个对象都具有这些属性和方法了
具体示例：
function PersonOne(name , age , gender){
this.name = name;
this.age = age;
this.gender = gender;
}
//向原型中添加sayName方法
PersonThree.prototype.sayName = function(){
alert("Hello大家好，我是:"+this.name);
};
//创建一个Person的实例
var per = new PersonThree("孙悟空",18,"男");
var per2 = new PersonThree("猪八戒",28,"男");
per.sayName();
per2.sayName();