不要在选项属性或回调上使用箭头函数，比如created: () => console.log(this.a)或vm.$watch('a', newValue => this.myMethod())。因为箭头函数并没有this，this会作为变量一直向上级词法作用域查找，直至找到为止，经常导致Uncaught TypeError: Cannot read property of undefined或Uncaught TypeError: this.myMethod is not a function之类的错误。

错误示范：

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<el-button type="primay" icon="el-icon-plus" @click="add"></el-button>
<p>{{count}}</p>
<script>
    const app = new Vue({
        // ...
        data: {
            count: 1
        },
        methods: {
            add: () => this.count++
        }
    });
</script>

正确示范：

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<script>
    const app = new Vue({
        // ...
        methods: {
            add: function () {
                this.count++
            },
            minus() {
                this.count--
            }
        }
    });
</script>