watch和computed均可以监控程序员想要监控的对象，当这些对象发生改变之后，可以触发回调函数做一些逻辑处理
watch监控自身属性变化
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<script src="https://cdn.jsdelivr.net/npm/vue"></script>
</head>
<body>
<div id="app">
<input type="text" v-model="firstName" />
<input type="text" v-model="lastName" /> {{fullName}}
</div>
<script>
new Vue({
el: ‘#app‘,
data: {
firstName: ‘hello‘,
lastName: ‘vue‘,
fullName: ‘hello.ve‘
},
watch: {
‘firstName‘: function(newval, oldval) {
// console.log(newval,oldval);
this.fullName = this.firstName + this.lastName;
},
‘lastName‘: function(newval, oldval) {
// console.log(newval,oldval);
this.fullName = this.firstName + this.lastName;
}
}
});
</script>
</body>
</html>
watch监控路由对象
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<script src="https://cdn.jsdelivr.net/npm/vue"></script>
<script src="https://unpkg.com/[email protected]/dist/vue-router.js"></script>
</head>
<body>
<div id="app">
<router-link to="/login">登录</router-link>
<router-link to="/register/value">注册</router-link>
<!--组件的显示占位域-->
<router-view></router-view>
</div>
<script>
//1.0 准备组件
var App = Vue.extend({});
var login = Vue.extend({
template: ‘<div><h3>登录</h3></div>‘
});
var register = Vue.extend({
template: ‘<div><h3>注册{{name}}</h3></div>‘,
data: function() {
return {
name: ‘‘
}
},
created: function() {
this.name = this.$route.params.name;
}
});
//2.0 实例化路由规则对象
var router = new VueRouter({
routes: [{
path: ‘/login‘,
component: login
},
{
path: ‘/register/:name‘,
component: register
},
{
path: ‘/‘,
//当路径为/时，重定向到/login
redirect: ‘/login‘
}
]
});
//3.0 开启路由对象
new Vue({
el: ‘#app‘,
router: router, //开启路由对象
watch: {
‘$route‘: function(newroute, oldroute) {
console.log(newroute, oldroute);
//可以在这个函数中获取到当前的路由规则字符串是什么
//那么就可以针对一些特定的页面做一些特定的处理
}
}
})
</script>
</body>
</html>
计算属性computed的特点
- 计算属性会依赖于他使用的data中的属性，只要是依赖的属性值有改变，则自动重新调用一下计算属性；
- 如果他所依赖的这些属性值没有发生改变，那么计算属性的值是从缓存中来的，而不是重新编译，那么性能要高一些，所以vue中尽可能使用computed替代watch。
案例演示
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<script src="https://cdn.jsdelivr.net/npm/vue"></script>
</head>
<body>
<div id="app">
<input type="text" v-model="firstName" />
<input type="text" v-model="lastName" />
{{fullName}}
</div>
<script>
new Vue({
el: ‘#app‘,
data: {
firstName: ‘hello‘,
lastName: ‘vue‘
},
computed: {
fullName: function() {
return this.firstName + this.lastName;
}
}
});
</script>
</body>
</html>
时间： 2024-08-02 07:02:02