监听属性

watch 

vue可以通过watch来监听属性值的变化。

<script src="https://how2j.cn/study/vue.min.js"></script>
     
<style>
table tr td{
    border:1px solid gray;
    padding:10px;
      
}
table{
    border-collapse:collapse;
    width:800px;
    table-layout:fixed;
}
tr.firstLine{
    background-color: lightGray;
}
</style>
   
<div id="div1">
     
    <table align="center" >
        <tr class="firstLine">
            <td>人民币</td>
            <td>美元</td>
        </tr>      
        <tr>
            <td align="center" colspan="2">
            汇率： <input type="number" v-model.number="exchange" />
            </td>
        </tr>
         
        <tr>
         
            <td align="center">
                ￥: <input type="number" v-model.number = "rmb"  />
            </td>
            <td align="center">
                $: <input type="number" v-model.number = "dollar"   />
            </td>
        </tr>
    </table>
   
</div>
      
<script>
    
new Vue({
      el: '#div1',
      data: {
          exchange:6.4,
          rmb:0,
          dollar:0
      },
      watch:{
          rmb:function(val) {
              this.rmb = val;
              this.dollar = this.rmb / this.exchange;
          },
          dollar:function(val) {
              this.dollar = val;
              this.rmb = this.dollar * this.exchange;
          },
      }
       
    })
      
</script>
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