watchEffect：自动监听值的变化
- 获取旧值时，不是很方便，建议用watch
html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
<div id="app">
爱好
<select v-model="hobby">
<option value="">请选择</option>
<option value="reading">阅读</option>
<option value="swimming">游泳</option>
<option value="running">跑步</option>
</select>
<hr>
年
<select v-model="date.year">
<option value="">请选择</option>
<option value="2021">2021</option>
<option value="2022">2022</option>
<option value="2023">2023</option>
<option value="2024">2024</option>
</select>
月
<select v-model="date.month">
<option value="">请选择</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
<option value="5">5</option>
<option value="6">6</option>
<option value="7">7</option>
<option value="8">8</option>
<option value="9">9</option>
<option value="10">10</option>
<option value="11">11</option>
<option value="12">12</option>
</select>
</div>
<script type="module">
import { createApp, reactive, ref, watchEffect } from './vue.esm-browser.js'
createApp({
setup() {
const hobby = ref("")
const date = reactive({
year: "",
month: ""
})
//自动监听
watchEffect(() => {
console.log("----- 自动监听开始")
console.log(hobby.value)
console.log(date.year, date.month)
console.log("自动监听结束 -----")
})
return {
date,
hobby
}
}
}).mount("#app")
</script>
</body>
</html>