一、基础计算模板

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Vue计算属性、方法、侦听器</title>
    <!--引入vue.js库-->
    <script src="../vue.js"></script>
</head>

<body>
<div id="root">
    {{firstName + " " + lastName}}
</div>

<script>
    var vm = new Vue({
        el: '#root',
        data: {
            firstName: "gb",
            lastName: "lfy"
        }
    });
</script>
</body>
</html>

升级一下

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Vue计算属性、方法、侦听器</title>
    <!--引入vue.js库-->
    <script src="../vue.js"></script>
</head>

<body>
<div id="root">
    {{firstName+" "+lastName}}
</div>

<script>
    var vm = new Vue({
        el: '#root',
        data: {
            firstName: "gb",
            lastName: "lfy"
        },
        //计算属性
        computed: {
            fallName: function () {
                return this.firstName + this.lastName;
            }
        }
    });
</script>
</body>
</html>

二、计算属性computed

有缓存机制，会用以前计算的结果
当计算的属性发生变化时会执行一次，当修改的数据不属于计算属性时，会从缓存中查询，不会执行。

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Vue计算属性、方法、侦听器</title>
    <!--引入vue.js库-->
    <script src="../vue.js"></script>
</head>

<body>
<div id="root">
    {{fullName}}
    {{age}}
</div>

<script>
    var vm = new Vue({
        el: '#root',
        data: {
            firstName: "gb",
            lastName: "lfy",
            age: 22
        },
        //计算属性
        computed: {
            fullName: function () {
                console.log("计算了一次")
                return this.firstName + this.lastName;
            }
        }
    });
</script>
</body>
</html>

在这里插入图片描述

三、方法methods

无缓存机制，不管修改什么输入都会执行一次

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Vue计算属性、方法、侦听器</title>
    <!--引入vue.js库-->
    <script src="../vue.js"></script>
</head>

<body>
<div id="root">
    {{fullName()}}
    {{age}}
</div>

<script>
    var vm = new Vue({
        el: '#root',
        data: {
            firstName: "gb",
            lastName: "lfy",
            age: 22
        },
        methods: {
            fullName: function () {
                console.log("计算了一次")
                return this.firstName + this.lastName;
            }
        }
    });
</script>
</body>
</html>

在这里插入图片描述

四、侦听器watch

和计算属性一样有缓存机制，只要我侦听的数据不发生改变，我就不会执行

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Vue计算属性、方法、侦听器</title>
    <!--引入vue.js库-->
    <script src="../vue.js"></script>
</head>

<body>
<div id="root">
    {{fullName()}}
    {{age}}
</div>

<script>
    var vm = new Vue({
        el: '#root',
        data: {
            firstName: "gb",
            lastName: "lfy",
            fullName: "gb lfy",
            age: 22
        },
        watch: {
            firstName: function () {
                console.log("计算了一次");
                this.firstName + this.lastName;
            },
            lastName: function () {
                console.log("计算了一次");
                this.firstName + this.lastName;
            },
        }
    });
</script>
</body>
</html>