this.$options.methods.test2();

new Vue({
    el: '#app',
  data: {
      test:111,
  },
  methods: {
      test1:function(){
            alert(this.test)
        },
        test2:function(){
            alert("this is test2")
            alert(this.test) //test3调用时弹出undefined
        },
        test3:function(){
            this.$options.methods.test2();//在test3中调用test2的方法
        }
  }
})