1.监视属性的基本用法
<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>天气案例-监视属性</title> <script type="text/javascript" src="../js/vue.js"></script> </head> <body> <div id="root"> <h1>今天的天气{{weather}}</h1> <button @click="changeWeather">改变天气</button> </div> </body> <!-- 监视属性watch 写法: 1.写在vm实例内部的watch配置 2.写在vm实例外部,vm.$watch 作用:被监视的属性改变时,回调函数执行,进行相关操作 注意:被监视的属性必须存在,计算属性也可以被监视 --> <script> const vm = new Vue({ el: "#root", data: { isHot: true }, computed: { weather() { return this.isHot ? "炎热" : "凉爽" } }, methods: { changeWeather() { this.isHot = !this.isHot } }, //监视属性的第一种写法,写在实例内部 watch: { isHot: { //immediate默认为false,当设置为true时会在一开始就调用一次handler immediate:true, //handler在被监视的属性变化时调用 handler(newValue, oldValue) { console.log("isHot变化了", oldValue, newValue) } } } }) //监视属性的第二种写法,写在vm实例外部,注意属性要加引号 vm.$watch("weather", { handler(newValue, oldValue) { console.log("weather变化了", oldValue, newValue) } }) </script> </html>
2.深度监视
<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>天气案例-深度监视</title> <script type="text/javascript" src="../js/vue.js"></script> </head> <body> <div id="root"> <h1>a的值为:{{numbers.a}}</h1> <button @click="numbers.a++">a加一</button> </div> </body> <!-- 深度监视 1.作用:监视有多个层级的属性,当对象内部值发生改变时,handler被调用 2.写法:watch中加一个配置项 deep:true --> <script> const vm = new Vue({ el: "#root", data: { numbers: { a: 1, b: 1, c: { c1: 1, c2: 1 } } }, //监视a的变化 watch: { "numbers.a": { handler(newValue, oldValue) { console.log("a变化了", oldValue, newValue) } }, //监视整个numbers的变化,numbers中任意属性发生改变,都会触发handler numbers : { deep: true, //开启深度监视 handler(newValue, oldValue) { console.log("numbers变化了", oldValue, newValue) } } } }) </script> </html>
3.监视属性简写
<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>天气案例-监视属性简写</title> <script type="text/javascript" src="../js/vue.js"></script> </head> <body> <div id="root"> <h1>今天的天气{{weather}}</h1> <button @click="changeWeather">改变天气</button> </div> </body> <!-- 简写的前提是除了handler不需要其他的配置项 --> <script> const vm = new Vue({ el: "#root", data: { isHot: true }, computed: { weather() { return this.isHot ? "炎热" : "凉爽" } }, methods: { changeWeather() { this.isHot = !this.isHot } }, watch: { isHot(newValue, oldValue) { console.log("isHot变化了", oldValue, newValue) } } }) vm.$watch("weather", function(newValue, oldValue) { console.log("weather变化了", oldValue, newValue) }) </script> </html>
(本文仅作个人学习记录用,如有纰漏敬请指正)
标签:Vue,watch,isHot,weather,numbers,oldValue,监视,newValue From: https://www.cnblogs.com/jmsstudy/p/17533351.html