1. 对象冒充
        实例：
            var Parent = function (username) {
                this.username = username
                this.getUserName = function () {
                    console.log('username:' + username)
                }
            }

            var Child = function (username, age) {
              this.method = Parent
              this.method(username)
              delete this.method

              this.getAge = function () {
                console.log('age:' + age)
              }
            }

            var p = new Parent('Tim')
            var s = new Child('Little Time', 5)

            p.getUserName()
            s.getUserName()
            s.getAge()

    

    2. call方式
        call方法是Function类中的方法
      call方法的第一个参数的值赋值给类(即方法)中出现的this
      call方法的第二个参数开始依次赋值给类(即方法)所接受的参数
        实例：
            var Parent = function (username) {
              this.username = username
              this.read = function () {
                console.log('read your ' + username)
              }
            }

            var Child = function (username, age) {
              Parent.call(this, username)
              this.age = age
              this.getAge = function () {
                console.log('appear your age :' + age)
              }
            }

            var p = new Parent('Tom')
            var s = new Child('little tom', 12)

            p.read()
            s.read()
            s.getAge()

  

 3. apply方式
    apply方法接受2个参数，
    第一个参数与call方法的第一个参数一样，即赋值给类(即方法)中出现的this
    第二个参数为数组类型，这个数组中的每个元素依次赋值给类(即方法)所接受的参数
        实例：
            var Parent = function (username) {
              this.username = username
              this.getName = function () {
                console.log('username:' + username)
              }
            }

            var Child = function (username, age) {
              Parent.apply(this, new Array(username))
              this.age = age
              this.getAge = function () {
                console.log('age:' + age)
              }
            }

            var p = new Parent('Shary')
            var s = new Child('little shary', 19)

            p.getName()
            s.getName()
            s.getAge()

    

    4. 原型链方式
        即子类通过prototype将所有在父类中通过prototype追加的属性和方法都追加到Child，从而实现了继承
        实例：
            var Parent = function () {}

            Parent.prototype.username = 'parent'
            Parent.prototype.getName = function () {
              console.log('username:' + this.username)
            }

            var Child = function () {}
            Child.prototype = new Parent()
            Child.prototype.getAge = function (age) {
              console.log('age:' + age)
            }

            var p = new Parent()
            p.getName()
            var s = new Child()
            s.getName()
            s.getAge(70)