（8）打鸡儿教你Vue.js

监听属性

监听属性 watch
通过 watch 来响应数据的变化

<div id = "app">
    <p style = "font-size:25px;">计数器: {{ counter }}</p>
    <button @click = "counter++" style = "font-size:25px;">点我</button>
</div>
<script type = "text/javascript">
var vm = new Vue({
    el: '#app',
    data: {
        counter: 1
    }
});
vm.$watch('counter', function(nval, oval) {
    alert('计数器值的变化 :' + oval + ' 变为 ' + nval + '!');
});
</script>

<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 = this.kilometers * 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>

<div id="app">
    <table>
    <tr>
        <th>序号</th>
        <th>商品名称</th>
        <th>商品价格</th>
        <th>购买数量</th>
        <th>操作</th>
    </tr>
    <tr v-for="iphone in Ip_Json">
        <td>{{ iphone.id }}</td>
        <td>{{ iphone.name }}</td>
        <td>{{ iphone.price }}</td>
        <td>
        <button v-bind:disabled="iphone.count === 0" v-on:click="iphone.count-=1">-</button>
        {{ iphone.count }}
        <button v-on:click="iphone.count+=1">+</button>
        </td>
        <td>
        <button v-on:click="iphone.count=0">移除</button>
        </td>
    </tr>
    </table>
    总价：${{totalPrice()}}
</div>

table {
    border: 1px solid black;
}
table {
     100%;
}

th {
    height: 50px;
}
th, td {
    border-bottom: 1px solid #ddd;
}

{{totalPrice()}}

methods:{
    totalPrice : function(){
      var totalP = 0;
      for (var i = 0,len = this.Ip_Json.length;i<len;i++) {
        totalP+=this.Ip_Json[i].price*this.Ip_Json[i].count;
      }
      return totalP;
    }
}

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