Vue学习之监听methods、watch及computed比较小结…

2019-08-14 10:03:08来源：博客园阅读 ()

一、三者之间的对比：

1、methods方法表示一个具体的操作，主要书写业务逻辑；

2、watch；一个对象，键是需要观察的表达式，值是对应回调函数。主要用来监听某些特定数据的变化，从而进行某些具体业务逻辑操作；可以看作是”computed"和“methods”的结合体；

3、computed属性的结果会被缓存，除非依赖的响应式属性变化才会重新计算。主要当作属性来使用。

二、methods：

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <title>methods实现名称拼接</title>
    <script src="./lib/vue.js"></script>
  </head>
  <body>
    <div id="app">
      <input type="text" v-model="firstname" @keyup="getFullname" /> +
      <input type="text" v-model="lastname" @keyup="getFullname" /> =
      <input type="text" v-model="fullname" />
    </div>
    <script>
      var vm = new Vue({
        el: "#app",
        data: {
          firstname: "",
          lastname: "",
          fullname: ""
        },
        methods: {
          getFullname() {
            this.fullname = this.firstname + "-" + this.lastname;
          }
        }
      });
    </script>
  </body>
</html>

2、watch:

使用这个属性，可以监视 data中指定数据的变化，然后触发这个watch中对应的function处理函数。

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <title>methods实现名称拼接</title>
    <script src="./lib/vue.js"></script>
  </head>
  <body>
    <div id="app">
      <!-- <input type="text" v-model="firstname" @keyup="getFullname" /> +
      <input type="text" v-model="lastname" @keyup="getFullname" /> = -->
      <input type="text" v-model="firstname" /> +
      <input type="text" v-model="lastname" /> =
      <input type="text" v-model="fullname" />
    </div>
    <script>
      var vm = new Vue({
        el: "#app",
        data: {
          firstname: "",
          lastname: "",
          fullname: ""
        },
        methods: {
          // getFullname() {
          //   this.fullname = this.firstname + "-" + this.lastname;
          // }
        },
        watch: {
          firstname: function(newVal, oldval) {
            this.fullname = newVal + "-" + this.lastname;
          },
          lastname: function(newVal) {
            this.fullname = this.firstname + "-" + newVal;
          }
        }
      });
    </script>
  </body>
</html>

3、watch监听路由地址的变化：

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <title>methods实现名称拼接</title>
    <script src="./lib/vue.js"></script>
    <!-- 1.导包 -->
    <script src="./lib/vue-router.js"></script>
  </head>
  <body>
    <div id="app">
      <router-link to="/login">登录</router-link>
      <router-link to="/register">注册</router-link>
      <router-view></router-view>
    </div>
    <script>
      //2.创建子组件
      var login = {
        template: "<h3>这是登录子组件</h3>"
      };

      var register = {
        template: "<h3>这是注册子组件</h3>"
      };
      //3.创建一个路由对象
      var router = new VueRouter({
        routes: [
          //路由规则数组
          { path: "/", redirect: "/login" },
          { path: "/login", component: login },
          { path: "/register", component: register }
        ],
        linkActiveClass: "myactive" //和激活有关的类
      });
      var vm = new Vue({
        el: "#app",
        data: {
     
        },
        methods: {},
   
        router,

  
        watch: {
      
          "$route.path": function(newVal, oldVal) {
            if (newVal === "/login") {
              console.log("欢迎进入登录页面");
            } else if (newVal === "/register") {
              console.log("欢迎进入注册页面");
            }
          }
        }
      });
    </script>
  </body>
</html>

4、computed：

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <title>methods实现名称拼接</title>
    <script src="./lib/vue.js"></script>
    <script src="./lib/vue-router.js"></script>
  </head>
  <body>
    <div id="app">
      <input type="text" v-model="firstname" /> +
      <input type="text" v-model="middlename" /> +
      <input type="text" v-model="lastname" /> =
      <input type="text" v-model="fullname" />
    </div>
    <script>
      var vm = new Vue({
        el: "#app",
        data: {
          firstname: "",
          middlename: "",
          lastname: ""
        },
        methods: {},
        watch: {},
        computed: {
          fullname: function() {
            console.log("ok");
            return this.firstname + "-" + this.middlename + "-" + this.lastname;
          }
        }
      });
    </script>
  </body>
</html>