JS继承

什么是继承

• 现实生活中的继承

• 程序中的继承

构造函数的属性继承：借用构造函数

 function Person (name, age) {
   this.type = 'human'
   this.name = name
   this.age = age
 }
 ​
 function Student (name, age) {
   // 借用构造函数继承属性成员 
   Person.call(this, name, age)
 }
 ​
 var s1 = Student('张三', 18)
 console.log(s1.type, s1.name, s1.age) // => human 张三 18

构造函数的原型方法继承：拷贝继承（for-in）

 function Person (name, age) {
   this.type = 'human'
   this.name = name
   this.age = age
 }
 ​
 Person.prototype.sayName = function () {
   console.log('hello ' + this.name)
 }
 ​
 function Student (name, age) {
   Person.call(this, name, age)
 }
 ​
 // 原型对象拷贝继承原型对象成员
 for(var key in Person.prototype) {
   Student.prototype[key] = Person.prototype[key]
 }
 ​
 var s1 = Student('张三', 18)
 ​
 s1.sayName() // => hello 张三

另一种继承方式：原型继承

 function Person (name, age) {
   this.type = 'human'
   this.name = name
   this.age = age
 }
 ​
 Person.prototype.sayName = function () {
   console.log('hello ' + this.name)
 }
 ​
 function Student (name, age) {
   Person.call(this, name, age)
 }
 ​
 // 利用原型的特性实现继承
 Student.prototype = new Person()
 ​
 var s1 = Student('张三', 18)
 ​
 console.log(s1.type) // => human
 ​
 s1.sayName() // => hello 张三