VueJs之判断与循环监听

watch 会实时监听数据变化并改变自身的值

<div id = "computed_props">
         千米 : <input type = "text" v-model = "kilometers">
         米 : <input type = "text" v-model = "meters">
      </div>
       <p id="info"></p>
      <script type = "text/javascript">
         var vm = new Vue({
            el: '#computed_props',
            data: {
               kilometers : 0,
               meters:0
            },
            methods: {
            },
            computed :{
            },
            watch : {
               kilometers:function(val) {
                  this.kilometers = val;
                  this.meters = val * 1000;
               },
               meters : function (val) {
                  this.kilometers = val/ 1000;
                  this.meters = val;
               }
            }
         });
         // $watch 是一个实例方法
        vm.$watch('kilometers', function (newValue, oldValue) {
            // 这个回调将在 vm.kilometers 改变后调用
            document.getElementById ("info").innerHTML = "修改前值为: " + oldValue + "，修改后值为: " + newValue;
        })
      </script>