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