Vuejs中关于computedmethodswatch，mounted的区别

Posted 漫思

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篇首语：本文由小常识网(cha138.com)小编为大家整理，主要介绍了Vuejs中关于computedmethodswatch，mounted的区别相关的知识，希望对你有一定的参考价值。

1.computed是在html DOM加载后马上执行的，如赋值；

2.methods则必须要有一定的触发条件才能执行，如点击事件；

3.watch呢？它用于观察Vue实例上的数据变动。对应一个对象，键是观察表达式，值是对应回调。值也可以是方法名，或者是对象，包含选项。

所以他们的执行顺序为：默认加载的时候先computed再watch，不执行methods；等触发某一事件后，则是：先methods再watch。

4.mounted是生命周期

5.created和mounted区别？

我们从图中看两个节点：
created:在模板渲染成html前调用，即通常初始化某些属性值，然后再渲染成视图。
mounted:在模板渲染成html后调用，通常是初始化页面完成后，再对html的dom节点进行一些需要的操作。
其实两者比较好理解，通常created使用的次数多，而mounted通常是在一些插件的使用或者组件的使用中进行操作，比如插件chart.js的使用: var ctx = document.getElementById(ID);通常会有这一步，而如果你写入组件中，你会发现在created中无法对chart进行一些初始化配置，一定要等这个html渲染完后才可以进行，那么mounted就是不二之选。下面看一个例子（用组件）。

我们用下面的例子再解说解说这些关系

HTML

复制代码
<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width,initial-scale=1.0">
    <title>my-vue</title>
    <style>
    body{
        font-family:"Microsoft YaHei";
    }
    #tab{
        width: 600px;
        margin: 0 auto;
    }
    .tab-tit{
        font-size: 0;
        width: 600px;
    }
    .tab-tit a{
        display: inline-block;
        height: 40px;
        line-height: 40px;
        font-size: 16px;
        width: 25%;
        text-align: center;
        background: #ccc;
        color: #333;
        text-decoration: none;
    }
    .tab-tit .cur{
        background: #09f;
        color: #fff;
    }
    .tab-con div{
        border: 1px solid #ccc;
        height: 400px;
        padding-top: 20px;
    }
    
        .fl{
            float: left;
        }
        .fr{
            float: right;
        }
       blockquote, body, dd, div, dl, dt, fieldset, form, h1, h2, h3, h4, h5, h6, img, input, li, ol, p, table, td, textarea, th, ul {
            margin: 0;
            padding: 0;
        }
       .clearfix{
          zoom: 1;
       }
        .clearfix:after {
            clear: both;
        }
        .clearfix:after {
            content: \'.\';
            display: block;
            overflow: hidden;
            visibility: hidden;
            font-size: 0;
            line-height: 0;
            width: 0;
            height: 0;
        }
        a{
            text-decoration: none;
            color: #333;
        }
        img{vertical-align: middle;}
        .page-shopping-cart {
            width: 1200px;
            margin: 50px auto;
            font-size: 14px;
            border: 1px solid #e3e3e3;
            border-top: 2px solid #317ee7; }
        .page-shopping-cart .cart-title {
            color: #317ee7;
            font-size: 16px;
            text-align: left;
            padding-left: 20px;
            line-height: 68px; }
        .page-shopping-cart .red-text {
            color: #e94826; }
        .page-shopping-cart .check-span {
            display: block;
            width: 24px;
            height: 20px;
               background: #fff;
    border: 1px solid #ccc; }
        .page-shopping-cart .check-span.check-true {
            background:#00f;
        }
        .page-shopping-cart .td-check {
            width: 70px; }
        .page-shopping-cart .td-product {
            width: 460px; }
        .page-shopping-cart .td-num, .page-shopping-cart .td-price, .page-shopping-cart .td-total {
            width: 160px; }
        .page-shopping-cart .td-do {
            width: 150px; }
        .page-shopping-cart .cart-product-title {
            text-align: center;
            height: 38px;
            line-height: 38px;
            padding: 0 20px;
            background: #f7f7f7;
            border-top: 1px solid #e3e3e3;
            border-bottom: 1px solid #e3e3e3; }
        .page-shopping-cart .cart-product-title .td-product {
            text-align: center;
            font-size: 14px; }
        .page-shopping-cart .cart-product-title .td-check {
            text-align: left; }
        .page-shopping-cart .cart-product-title .td-check .check-span {
            margin: 9px 6px 0 0; }
        .page-shopping-cart .cart-product {
            padding: 0 20px;
            text-align: center; }
        .page-shopping-cart .cart-product table {
            width: 100%;
            text-align: center;
            font-size: 14px; }
        .page-shopping-cart .cart-product table td {
            padding: 20px 0; }
        .page-shopping-cart .cart-product table tr {
            border-bottom: 1px dashed #e3e3e3; }
        .page-shopping-cart .cart-product table tr:last-child {
            border-bottom: none; }
        .page-shopping-cart .cart-product table .product-num {
            border: 1px solid #e3e3e3;
            display: inline-block;
            text-align: center; }
        .page-shopping-cart .cart-product table .product-num .num-do {
            width: 24px;
            height: 28px;
            display: block;
            background: #f7f7f7; }
        .page-shopping-cart .cart-product table .product-num .num-reduce span {
            background: url("shopping_cart.png") no-repeat -40px -22px;
            display: block;
            width: 6px;
            height: 2px;
            margin: 13px auto 0 auto; }
        .page-shopping-cart .cart-product table .product-num .num-add span {
            background: url("shopping_cart.png") no-repeat -60px -22px;
            display: block;
            width: 8px;
            height: 8px;
            margin: 10px auto 0 auto; }
        .page-shopping-cart .cart-product table .product-num .num-input {
            width: 42px;
            height: 28px;
            line-height: 28px;
            border: none;
            text-align: center; }
        .page-shopping-cart .cart-product table .td-product {
            text-align: left;
            font-size: 12px;
            line-height: 20px; }
        .page-shopping-cart .cart-product table .td-product img {
            border: 1px solid #e3e3e3;
            margin-right: 10px; }
        .page-shopping-cart .cart-product table .td-product .product-info {
            display: inline-block;
            vertical-align: middle; }
        .page-shopping-cart .cart-product table .td-do {
            font-size: 12px; }
        .page-shopping-cart .cart-product-info {
            height: 50px;
            line-height: 50px;
            background: #f7f7f7;
            padding-left: 20px; }
        .page-shopping-cart .cart-product-info .delect-product {
            color: #666; }
        .page-shopping-cart .cart-product-info .delect-product span {
            display: inline-block;
            vertical-align: top;
            margin: 18px 8px 0 0;
            width: 13px;
            height: 15px;
            background: url("shopping_cart.png") no-repeat -60px 0; }
        .page-shopping-cart .cart-product-info .product-total {
            font-size: 14px;
            color: #e94826; }
        .page-shopping-cart .cart-product-info .product-total span {
            font-size: 20px; }
        .page-shopping-cart .cart-product-info .check-num {
            color: #333; }
        .page-shopping-cart .cart-product-info .check-num span {
            color: #e94826; }
        .page-shopping-cart .cart-product-info .keep-shopping {
            color: #666;
            margin-left: 40px; }
        .page-shopping-cart .cart-product-info .keep-shopping span {
            display: inline-block;
            vertical-align: top;
            margin: 18px 8px 0 0;
            width: 15px;
            height: 15px;
            background: url("shopping_cart.png") no-repeat -40px 0; }
        .page-shopping-cart .cart-product-info .btn-buy {
            height: 50px;
            color: #fff;
            font-size: 20px;
            display: block;
            width: 110px;
            background: #ff7700;
            text-align: center;
            margin-left: 30px; }
        .page-shopping-cart .cart-worder {
            padding: 20px; }
        .page-shopping-cart .cart-worder .choose-worder {
            color: #fff;
            display: block;
            background: #39e;
            width: 140px;
            height: 40px;
            line-height: 40px;
            border-radius: 4px;
            text-align: center;
            margin-right: 20px; }
        .page-shopping-cart .cart-worder .choose-worder span {
            display: inline-block;
            vertical-align: top;
            margin: 9px 10px 0 0;
            width: 22px;
            height: 22px;
            background: url("shopping_cart.png") no-repeat -92px 0; }
        .page-shopping-cart .cart-worder .worker-info {
            color: #666; }
        .page-shopping-cart .cart-worder .worker-info img {
            border-radius: 100%;
            margin-right: 10px; }
        .page-shopping-cart .cart-worder .worker-info span {
            color: #000; }

        .choose-worker-box {
            width: 620px;
            background: #fff; }
        .choose-worker-box .box-title {
            height: 40px;
            line-height: 40px;
            background: #F7F7F7;
            text-align: center;
            position: relative;
            font-size: 14px; }
        .choose-worker-box .box-title a {
            display: block;
            position: absolute;
            top: 15px;
            right: 16px;
            width: 10px;
            height: 10px;
            background: url("shopping_cart.png") no-repeat -80px 0; }
        .choose-worker-box .box-title a:hover {
            background: url("shopping_cart.png") no-repeat -80px -22px; }
        .choose-worker-box .worker-list {
            padding-top: 30px;
            height: 134px;
            overflow-y: auto; }
        .choose-worker-box .worker-list li {
            float: left;
            width: 25%;
            text-align: center;
            margin-bottom: 30px; }
        .choose-worker-box .worker-list li p {
            margin-top: 8px; }
        .choose-worker-box .worker-list li.cur a {
            color: #f70; }
        .choose-worker-box .worker-list li.cur a img {
            border: 1px solid #f70; }
        .choose-worker-box .worker-list li a:hover {
            color: #f70; }
        .choose-worker-box .worker-list li a:hover img {
            border: 1px solid #f70; }
        .choose-worker-box .worker-list li img {
            border: 1px solid #fff;
            border-radius: 100%; }
        .check-true{
          background:#00f;
        }
</style>
  </head>
  <body>
    <div id="tab">
        <div class="tab-tit">
            <!--点击设置curId的值  如果curId等于0，第一个a添加cur类名，如果curId等于1，第二个a添加cur类名，以此类推。添加了cur类名，a就会改变样式 @click,:class ,v-show这三个是vue常用的指令或添加事件的方式-->
            <a href="javascript:;" @click="curId=0" :class="{\'cur\':curId===0}">html</a>
            <a href="javascript:;" @click="curId=1" :class="{\'cur\':curId===1}">css</a>
            <a href="javascript:;" @click="curId=2" :class="{\'cur\':curId===2}">javascript</a>
            <a href="javascript:;" @click="curId=3" :class="{\'cur\':curId===3}">vue</a>
        </div>
        <div class="tab-con">
            <!--根据curId的值显示div,如果curId等于0，第一个div显示，其它三个div不显示。如果curId等于1，第二个div显示，其它三个div不显示。以此类推-->
            <div v-show="curId===0">
                html<br/>
            </div>
            <div v-show="curId===1">
                css
            </div>
            <div v-show="curId===2">
                javascript
            </div>
            <div v-show="curId===3">
                vue
            </div>
        </div>
    </div>
   
<div class="page-shopping-cart" id="shopping-cart">
    <h4 class="cart-title">购物清单</h4>
    <div class="cart-product-title clearfix">
        <div class="td-check fl"><span class="check-span fl check-all" :class="{\'check-true\':isSelectAll}" @click="selectProduct(isSelectAll)"></span>全选</div>
        <div class="td-product fl">商品</div>
        <div class="td-num fl">数量</div>
        <div class="td-price fl">单价(元)</div>
        <div class="td-total fl">金额(元)</div>
        <div class="td-do fl">操作</div>
    </div>
    <div class="cart-product clearfix">
        <table>
            <tbody>
            <!--遍历的时候带上索引-->
            <tr v-for="(item,index) in productList">
                <td class="td-check"><span class="check-span" @click="item.select=!item.select" :class="{\'check-true\':item.select}"></span></td>
                <td class="td-product"><img :src="item.pro_img" width="98" height="98">
                    <div class="product-info">
                        <h6>{{item.pro_name}}</h6>
                        <p>品牌：{{item.pro_brand}}&nbsp;&nbsp;产地：{{item.pro_place}}</p>
                        <p>规格/纯度:{{item.pro_purity}}&nbsp;&nbsp;起定量：{{item.pro_min}}</p>
                        <p>配送仓储：{{item.pro_depot}}</p>
                    </div>
                    <div class="clearfix"></div>
                </td>
                <td class="td-num">
                    <div class="product-num">
                        <a href="javascript:;" class="num-reduce num-do fl" @click="item.pro_num>0?item.pro_num--:\'\'"><span>-</span></a>
                        <input type="text" class="num-input" v-model="item.pro_num">
                        <a href="javascript:;" class="num-add num-do fr" @click="item.pro_num++"><span>+</span></a>
                    </div>
                </td>
                <td class="td-price">
                    <p class="red-text">￥<span class="price-text">{{item.pro_price.toFixed(2)}}</span></p>
                </td>
                <td class="td-total">
                    <p class="red-text">￥<span class="total-text">{{item.pro_price*item.pro_num}}</span>.00</p>
                </td>
                <td class="td-do"><a href="javascript:;" class="product-delect" @click="deleteOneProduct(index)">删除</a></td>
            </tr>
            </tbody>
        </table>
    </div>
    <div class="cart-product-info">
        <a class="delect-product" href="javascript:;" @click="deleteProduct"><span></span>删除所选商品</a>
        <a class="keep-shopping" href="#"><span></span>继续购物</a>
        <a class="btn-buy fr" href="javascript:;">去结算</a>
        <p class="fr product-total">￥<span>{{getTotal.totalPrice}}</span></p>
        <p class="fr check-num"><span>{{getTotal.totalNum}}</span>件商品总计（不含运费）：</p>
    </div>
</div>
   
   
   
  </body>
</html>
复制代码

JS 

复制代码
// The Vue build version to load with the `import` command
// (runtime-only or standalone) has been set in webpack.base.conf with an alias.
import Vue from \'vue\'
import App from \'./App\'
import router from \'./router\'

Vue.config.productionTip = false

/* eslint-disable no-new */
new Vue({
        el: \'#tab\',
        data: {
            curId: 0
        },
        computed: {},
        methods: {},
        mounted: function () {
        }
    })
new Vue({
        el: \'#shopping-cart\',
        data: {
            productList: [
                {
                    \'pro_name\': \'【斯文】甘油 | 丙三醇\',//产品名称
                    \'pro_brand\': \'skc\',//品牌名称
                    \'pro_place\': \'韩国\',//产地
                    \'pro_purity\': \'99.7%\',//规格
                    \'pro_min\': "215千克",//最小起订量
                    \'pro_depot\': \'上海仓海仓储\',//所在仓库
                    \'pro_num\': 3,//数量
                    \'pro_img\': \'../../images/ucenter/testimg.jpg\',//图片链接
                    \'pro_price\': 800//单价
                },
                {
                    \'pro_name\': \'【斯文】甘油 | 丙三醇\',//产品名称
                    \'pro_brand\': \'skc\',//品牌名称
                    \'pro_place\': \'韩国\',//产地
                    \'pro_purity\': \'99.7%\',//规格
                    \'pro_min\': "215千克",//最小起订量
                    \'pro_depot\': \'上海仓海仓储\',//所在仓库
                    \'pro_num\': 3,//数量
                    \'pro_img\': \'../../images/ucenter/testimg.jpg\',//图片链接
                    \'pro_price\': 800//单价
                },
                {
                    \'pro_name\': \'【斯文】甘油 | 丙三醇\',//产品名称
                    \'pro_brand\': \'skc\',//品牌名称
                    \'pro_place\': \'韩国\',//产地
                    \'pro_purity\': \'99.7%\',//规格
                    \'pro_min\': "215千克",//最小起订量
                    \'pro_depot\': \'上海仓海仓储\',//所在仓库
                    \'pro_num\': 3,//数量
                    \'pro_img\': \'../../images/ucenter/testimg.jpg\',//图片链接
                    \'pro_price\': 800//单价
                }
            ]
        },
        computed: {
            //检测是否全选
            isSelectAll:function(){
                //如果productList中每一条数据的select都为true，返回true，否则返回false;
                return this.productList.every(function (val) { return val.select});
            },
            //获取总价和产品总件数
            getTotal:function(){
                //获取productList中select为true的数据。
                var _proList=this.productList.filter(function (val) { return val.select}),totalPrice=0;
                for(var i=0,len=_proList.length;i<len;i++){
                    //总价累加
                    totalPrice+=_proList[i].pro_num*_proList[i].pro_price;
                }
                //选择产品的件数就是_proList.length，总价就是totalPrice
                return {totalNum:_proList.length,totalPrice:totalPrice}
            }
        },
        methods: {
            //全选与取消全选
            selectProduct:function(_isSelect){
                //遍历productList，全部取反
                for (var i = 0, len = this.productList.length; i < len; i++) {
                    this.productList[i].select = !_isSelect;
                }
            },
            //删除已经选中(select=true)的产品
            deleteProduct:function () {
                this.productList=this.productList.filter(function (item) {return !item.select})
            },
            //删除单条产品
            deleteOneProduct:function (index) {
                //根据索引删除productList的记录
                this.productList.splice(index,1);
            },
        },
        mounted: function () {
            var _this=this;
            //为productList添加select（是否选中）字段，初始值为true
            this.productList.map(function (item) {
                _this.$set(item, \'select\', true);
            })
        }
    })
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