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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<script src="D:\Github\vue\lib\vue.js"></script>

<script>
window.onload = function() {
var suggestion = ['T恤短衫','夹克长裙','棉衣羽绒服'];
var app = new Vue({
el: "#app",
data: {
temperature: 15,
suggestion: "夹克长裙"
},
methods: {
add() {
this.temperature += 5
},
reduce() {
this.temperature -= 5
}
},
// watch: {
// // 不应该使用箭头函数定义侦听属性watch,因为箭头函数绑定了父级作用域的上下文,所以this将不会指向Vue实例,即找不到this.suggerstion属性
// temperature: function(newVal,oldVal) {
// if(newVal >= 26) {
// this.suggestion = suggestion[0]
// } else if (newVal < 26 && newVal >= 0) {
// this.suggestion = suggestion[1]
// } else {
// this.suggestion = suggestion[2]
// }
// }
// }
})

app.$watch('temperature', function(newVal,oldVal) {
if(newVal >= 26) {
this.suggestion = suggestion[0]
} else if (newVal < 26 && newVal >= 0) {
this.suggestion = suggestion[1]
} else {
this.suggestion = suggestion[2]
}
})
}
</script>
</head>
<body>
<div id="app">
<p>今日温度: {{temperature}}</p>
<p>穿衣建议: {{suggestion}}</p>
<p>
<button @click="add">增加温度</button>
<button @click="reduce">减少温度</button>
</p>
</div>
</body>
</html>