参考：传送门1
传送门2
传送门3

参考了官方文档，总结如下：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script src="./vue.js"></script>
</head>
<body>
    <div id="example">


    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>input</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>text<span class="token punctuation">"</span></span> <span class="token attr-name">v-model</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>firstname<span class="token punctuation">"</span></span><span class="token punctuation">&gt;</span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>input</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>text<span class="token punctuation">"</span></span> <span class="token attr-name">v-model</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>lastname<span class="token punctuation">"</span></span><span class="token punctuation">&gt;</span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>input</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>text<span class="token punctuation">"</span></span> <span class="token attr-name">v-model</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>fullname<span class="token punctuation">"</span></span><span class="token punctuation">&gt;</span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>input</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>button<span class="token punctuation">"</span></span> <span class="token attr-name">@click</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>getFullname()<span class="token punctuation">"</span></span> <span class="token attr-name">value</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>点我<span class="token punctuation">"</span></span><span class="token punctuation">&gt;</span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>
</body>
<script>
var vm = new Vue({
        el:'#example',
        data:{
            firstname:'xiao',
            lastname:'ming',
            fullname:''
        },
        computed: {// 直接计算它下面属性，不用管他有没有被动，至于牵涉到的属性都是直接计算得的
            fullname: function () {
                // this 指向 vm 实例
                // return this.firstname.split('').reverse().join('')
                return this.firstname+this.lastname;
            }
        },
        watch:{// 只有有动watch下面动属性了才会触发他的操作
            fullname:function () {
                this.fullname = this.firstname+this.lastname;
            }
        },
        methods: {
            getFullname:function(){
                this.fullname=this.firstname+this.lastname;
            }
        }
    });


</script>
</html>