未捕获的类型错误：无法在方法中读取 null 的属性“classList”

Question

我对 VueJS 和 BootstrapVue 还很陌生，我已经创建了一个方法，使用导航栏组件中的事件滚动来替换

路由器链接精确激活

与

精确链接更改

虽然它有效，但我得到了问题

未捕获的类型错误：无法读取属性 'classList' of null"

问题在于这两个代码：

link.classList.add("exact-link-change")

cLink.classList.add("router-link-exact-active")

这是组件中的脚本文件：

<script type="text/javascript">
    export default{
        name:'Navbar',
    data(){
        return{

        }
    },
    methods:{
        handleScroll (event) {
            let header = document.querySelector(".nav");
            let link = document.querySelector(".router-link-exact-active");
            let cLink = document.querySelector(".exact-link-change");
            if (window.scrollY > 100) {
                header.classList.add("nav--bgscroll") 
                link.classList.add("exact-link-change")
                link.classList.remove("router-link-exact-active")
            } 
            else{
                header.classList.remove("nav--bgscroll") 
                cLink.classList.add("router-link-exact-active")
                cLink.classList.remove("exact-link-change")
            } 
        },
    },
    created () {
      window.addEventListener('scroll', this.handleScroll);
    },
    destroyed () {
      window.removeEventListener('scroll', this.handleScroll);
    }
}
</script>

这是 HTML：

<template>
      <b-navbar toggleable= "lg" type="light"  class = "nav" @scroll = "handleScroll">
          <b-navbar-brand class = "title"> Aquafarm Beach Resort</b-navbar-brand>
          <b-navbar-toggle target="nav-collapse"></b-navbar-toggle>

              <b-collapse id="nav-collapse" is-nav>
                <b-navbar-nav>
                  <b-nav-item><b-link to ="/" active >Home</b-link></b-nav-item>
                  <b-nav-item><b-link :to="{name: 'Rooms'}">Rooms</b-link></b-nav-item>
                  <b-nav-item><b-link :to="{name: 'About' }">About</b-link></b-nav-item>
                  <b-nav-item><b-link :to="{name: 'ContactUs'}">Contact Us</b-link></b-nav-item>
                </b-navbar-nav>

                <b-navbar-nav class="ml-auto" >
                  <b-button variant= "outline-dark" :to="{name: 'Booking'}">Book Now</b-button>
                </b-navbar-nav>
              </b-collapse>
      </b-navbar> 
</template>

Answer 1

BootstrapVue 中接受to 属性的大多数组件也具有active-class 和exact-active-class 属性，它们允许您指示组件应用与默认值不同的类名。你也不需要在<b-nav-item> 中放置<b-link>，因为<b-nav-item> 支持to 属性：

<b-navbar-nav>
  <b-nav-item to ="/" active exact-active-class="exact-link-change">Home</b-nav-item>
  <b-nav-item :to="{name: 'Rooms'}" exact-active-class="exact-link-change">Rooms</b-nav-item>
  <b-nav-item :to="{name: 'About' }" exact-active-class="exact-link-change">About</b-nav-item>
  <b-nav-item :to="{name: 'ContactUs'}" exact-active-class="exact-link-change">Contact Us</b-nav-item>
</b-navbar-nav>

exact-active-class 和 active-class 属性是反应式的，因此您可以将它们 v-bind 到计算的属性上，该属性根据某些条件返回特定的类名。

我建议阅读以下内容：

• https://bootstrap-vue.js.org/docs/reference/router-links/
• https://bootstrap-vue.js.org/docs/components/nav#comp-ref-b-nav-item

<template>
  <b-navbar-nav>
    <b-nav-item to ="/" :exact-active-class="activeClass">Home</b-nav-item>
    <b-nav-item :to="{name: 'Rooms'}" :exact-active-class="activeClass">Rooms</b-nav-item>
    <b-nav-item :to="{name: 'About' }" :exact-active-class="activeClass">About</b-nav-item>
    <b-nav-item :to="{name: 'ContactUs'}" :exact-active-class="activeClass">Contact Us</b-nav-item>
  </b-navbar-nav>
</template>

<script>
export default {
  data(){
    return{
      isPast100Px: false
    }
  },
  computed: {
    activeClass() {
      return this.isPast100px ? 'exact-link-change' : ''
    }
  }
  methods:{
    handleScroll (event) {
      this.isPast100Px = window.scrollY > 100
    },
  },
  beforeMount () {
    window.addEventListener('scroll', this.handleScroll);
  },
  destroyed () {
    window.removeEventListener('scroll', this.handleScroll);
  }
}
</script>