classList对于已定义类的元素不确定

Question

我正在尝试将类添加和删除为VueJS中的元素。我的代码中缺少的链接是类列表返回未定义。为什么是这样？谢谢。我正在用jQuery getElementByid速记抓住元素$

<template>
    <div class="form-field" id="outerdiv">
        <div class="form-field__control">
            <label for="exampleField" class="form-field__label">{{fieldLabel}}</label>
            <input id="exampleField"  v-model="fieldContent" @blur="setActive(false, $event)" @focus="setActive(true, $event)"
            type="text" class="form-field__input" />
        </div>
    </div>    
</template>
<script>
import $ from "jquery";
export default {
    name: "FormField",
    props: {fieldContent: String, fieldLabel: String},
    methods: {
        setActive(active, event) {
            console.log("this.fieldContent: "+this.fieldContent);
            const formField = event.target.parentNode.parentNode
            if (active) {
                formField.classList.add('form-field--is-active')
            } else {
                formField.classList.remove('form-field--is-active')
                event.target.value === '' ? 
                formField.classList.remove('form-field--is-filled') : 
                formField.classList.add('form-field--is-filled')
            }
        }
    },
    updated() {
        console.log("in initialize form field");
        console.log("this.fieldContent: "+this.fieldContent);
        console.log("result from shorthand getElementById: "+$("#outerdiv"));
        console.log("classList of element: "+ $("#outerdiv").classList);
        this.fieldContent === '' ?
        $("#outerdiv").classList.remove('form-field--is-filled'):
        $("#outerdiv").classList.add('form-field--is-filled')
    }
}
</script>
<style>
    .form-control{
        border-style: none;
        width: 100%;
        height: 34px;
        padding: 0px 0px;
        font-size: 20px;
    }
</style>

Answer 1

虽然解决了主要问题，但您可以简化代码，同时通过以Vue方式进行jQuery的需求。

通过使用类绑定，您可以用计算的道具替换IF，如果您需要直接访问元素，则可以使用参考。

只需运行以下片段即可看到这些概念：

new Vue({
  el: '#app',
  data: {
    fieldContent: '', 
    fieldLabel: '',
    active: false,
  },
  computed: {
    classList() {
      return {
        'form-field--is-filled': this.fieldContent !== '',
        'form-field--is-active': this.active,
      };
    }
  },
  methods: {
    setActive(active, event) {
      console.log("this.fieldContent: "+this.fieldContent);
      this.active = active;
    }
  },
  updated() {
    console.log("in initialize form field");
    console.log("this.fieldContent: "+this.fieldContent);
    console.log("result from shorthand getElementById: ", this.$refs.outerDiv);
    console.log("classList of element: "+ this.$refs.outerDiv.classList);
  }
});

.form-control{
  border-style: none;
  width: 100%;
  height: 34px;
  padding: 0px 0px;
  font-size: 20px;
}
.form-field--is-active {
  border: 1px solid green;
}
.form-field--is-filled {
  outline: 1px dotted blue;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.17/vue.js"></script>
<div id="app">
    <div class="form-field" id="outerdiv" :class="classList" ref="outerDiv">
        <div class="form-field__control">
            <label for="exampleField" class="form-field__label">{{fieldLabel}}</label>
            <input id="exampleField"  v-model="fieldContent" @blur="setActive(false, $event)" @focus="setActive(true, $event)"
            type="text" class="form-field__input" />
        </div>
    </div>    
</div>