JS 继承

1 原型链继承

	//父类
	function Person(name,age){
		this.name = name || 'unknow'
		this.age = age || 0
	}

	//子类
	function Student(name){
		this.name = name
		this.score = 80
	}

	//继承
	Student.prototype = new Person();
	Student.prototype.constructor = Student;
	

	var stu = new Student('lucy');
	console.log(stu.name);  //lucy  --子类覆盖父类的属性
	console.log(stu.age);   // 0    --父类的属性
	console.log(stu.score);  // 80   --子类自己的属性


*原型继承共享引用类型(方法)*
共享方法可以,因为方法本身代码不变,就是被共享的. 但有些引用类型自身变化,如下
	//父类
	function Person(){
		this.hobbies = ['music','reading']
	}

	//子类
	function Student(){
	}

	//继承
	Student.prototype = new Person();
	Student.prototype.constructor = Student;

	var stu1 = new Student();
	var stu2 = new Student();

	stu1.hobbies.push('basketball');

	console.log(stu1.hobbies);  // ["music", "reading", "basketball"]
	console.log(stu2.hobbies);  //  ["music", "reading", "basketball"]

2 构造函数继承

*构造函数不共享引用类型和方法*
	
	//父类
	function Person(){
		this.hobbies = ['music','reading']
	}

	//子类
	function Student(){
		Person.call(this);
	}

	var stu1 = new Student();
	var stu2 = new Student();

	stu1.hobbies.push('basketball');

	console.log(stu1.hobbies);  // ["music", "reading", "basketball"]
	console.log(stu2.hobbies);  //  ["music", "reading"]

*构造函数可以给父类传参*
	//父类
	function Person(name){
		this.name = name;
	}

	//子类
	function Student(name){
		Person.call(this,name);  //传参Person(name)
	}

	var stu1 = new Student('lucy');
	var stu2 = new Student('lili');


	console.log(stu1.name);  //  lucy
	console.log(stu2.name);  //  lili

3 组合继承
某些引用类型属性使用构造函数继承不共享，方法使用原型链继承共享。
不论是构造函数还是原型链, 基本类型都是不共享的(基本类型与引用类型赋值的区别)

	//父类
	function Person(name){
		this.hobbies = ['music','reading'];
	}

	Person.prototype.say = function(){
		console.log('i am a person');
	}
	//子类
	function Student(name){
		Person.call(this);  //构造函数继承（继承属性）本地hobbies
	}

	Student.prototype = new Person();  //原型继承（继承方法） 原型链hobbies和say
	Student.prototype.constructor = Student;

	//其实是本地hobbies比原型链的hobbies优先,实现组合继承
	var stu1 = new Student('lucy');
	var stu2 = new Student('lili');

	stu1.hobbies.push('basketball');

	console.log(stu1.hobbies);  // ["music", "reading", "basketball"]
	console.log(stu2.hobbies);  // ["music", "reading"]

	console.log(stu1.say === stu2.say);  // true