watch监听的数据对应的函数,有两个参数,一个是在原有的值上增加的值,一个是原有的值
1 <!DOCTYPE html> 2 <html lang="en"> 3 <head> 4 <meta charset="UTF-8"> 5 <title>Title</title> 6 <script src="../util/vue-2.4.0.js"></script> 7 </head> 8 <body> 9 <div id="test"> 10 <input type="text" v-model="firstname"> + 11 <input type="text" v-model="lastname"> = 12 <input type="text" v-model="fullname"> 13 </div> 14 <script> 15 var vm1 = new Vue({ 16 el:"#test", 17 data:{ 18 firstname:"", 19 lastname:"", 20 fullname:"" 21 }, 22 methods:{}, 23 created(){}, 24 components:{}, 25 router:{}, 26 watch:{ 27 "firstname":function (newValue,oldValue) { 28 this.fullname = newValue + this.lastname 29 }, 30 "lastname":function (newValue,oldValue) { 31 this.fullname = this.firstname + newValue 32 } 33 } 34 }) 35 </script> 36 </body> 37 </html>