js学习笔记01

1 传值和传址：

js的数据赋值根据数据类型来判别，

传值：数据值，布尔型，字符型基本数据

传址：数据，hash对象，赋值的过程会用内存地址赋值，影响原数据。解决方案：遍历数组和对象赋值，相当于传值。

prototype也是hash对象，赋值的话也会传址.

function Animal(name){
this.name=name;
this.type="animal";
}
Animal.prototype.say=function(){
console.log(this.name+"type is:"+this.type);
}
function Bird(name){
Animal.call(this,name);
}

Bird.prototype.fly=function(){
console.log("I'm flying");

}
Bird.prototype=Animal.prototype;
var mybird=new Bird("bird");
var mydog=new Animal();

mybird.fly();//I'm flying

mydog.fly();//I'm flying

Animal的prototype也会带有fly()方法。

解决方案：

（1）上述类似的，遍历赋值

function Animal(name){
this.name=name;
this.type="animal";
}
Animal.prototype.say=function(){
console.log(this.name+"type is:"+this.type);
}
function Bird(name){
Animal.call(this,name);
}

for(var p in Animal)
{
Bird.prototype[p]=Animal.prototype[p];
}
Bird.prototype.fly=function(){
console.log("I'm flying");

}

var mybird=new Bird("bird");
var mydog=new Animal();

mybird.fly();//I'm flying

mydog.fly();// Uncaught TypeError: undefined is not a function 

（2）把bird作为Animal的一个实例

function Animal(name){
this.name=name;
this.type="animal";
}
Animal.prototype.say=function(){
console.log(this.name+"type is:"+this.type);
}
function Bird(name){
Animal.call(this,name);
}

Bird.prototype=new Animal();
Bird.prototype.constructor=Bird;
Bird.prototype.fly=function(){
console.log("I'm flying");
}

var mybird=new Bird("bird");
var mydog=new Animal();

mybird.fly();//I'm flying

mydog.fly(); // Uncaught TypeError: undefined is not a function 

（3）把方法封装起来

function extend(subClass,superClass){
var F=function(){};
F.prototype=superClass.prototype;
subClass.prototype=new F();
subClass.prototype.contructor=subClass;

}

function Animal(name){
this.name=name;
this.type="animal";
}
Animal.prototype.say=function(){
alert(this.name+"type:"+this.type);
}
function Bird(name){
this.name=name;
this.type="bird";
}
extend(Bird,Object);
Bird.prototype.fly=function(){
alert("I'm flying");
}

var canary=new Bird("xiaocui");
var animal= new Animal();
canary.say();
canary.fly();

2 数据类型

undefined，null,"",0，转换为逻辑值为false，其他(简单类型，对象，函数)都为true。在这五个之中，undefined==null为true，其实均为false;