SOURCE

window.onload = function() {
  let vm = new Vue({
		el: "#app",
    data: {
      name: '123',
      info: {
        userName: '12',
        userPass: '2323'
      }
    },
    watch: {
      name: {
        handler (n) {
          console.log(n)
        },
        immediate: true
      },
      info: {
        handler (n, o) {
          	console.log(1)
        },
        immediate: true
      }
    },
    mounted () {
      this.info.userName = 'zhangli'
    }
  })
}

<div id="app">
  <input type="text" v-model="info.userName" />
  <input type="text" v-model="info.userPass"/>
</div>