How does vue get the dom value to be null

As a Vue developer, getting the value of a DOM element is a problem we often encounter. However, what should we do when the value we get is null? This article will introduce several methods on how Vue obtains the DOM value of null to help developers better handle such situations.

What is a DOM value that is null?

Before introducing the method of obtaining the DOM value of null, we first need to understand what the DOM value of null is.

DOM (Document Object Model), the document object model, parses HTML and XML documents into a series of nodes (including element nodes, attribute nodes, text nodes, etc.) and objects, thereby creating a Document objects that can be manipulated.

When we obtain the DOM element in Vue through $refs or other methods, for some reasons, the element may not be rendered or mounted. At this time, the obtained DOM element The value is null.

How to get the DOM value to be null

1. Use this.$nextTick()

In Vue, when some DOM elements need When the Vue instance is initialized after rendering, we can use the this.$nextTick() method to run our code after the DOM is updated.

mounted() {
  this.$nextTick(() => {
    const dom = this.$refs.dom;
    if (dom === null) {
      console.log("DOM值为null");
    }
  });
}

2. Use the v-if directive

When using Vue, we usually use the v-if directive before rendering the DOM element Make conditional judgments to control whether DOM elements are rendered. We can use this mechanism to get the DOM value as null.

<template>
  <div>
    <child ref="child" v-if="show"></child>
  </div>
</template>

<script>
export default {
  data() {
    return {
      show: false
    }
  },
  mounted() {
    this.show = true;
    this.$nextTick(() => {
      const dom = this.$refs.child.$el;
      if (dom === null) {
        console.log("DOM值为null");
      }
    });
  }
}
</script>

In the above code, we initially set show to false so that the child component does not render. Then set show to true in the mounted life cycle hook, and then use the $nextTick() method to get the DOM after the DOM is updated The value of the element and make a judgment.

3. Use the v-cloak directive

v-cloak directive can be used to hide uncompiled Mustache templates during the initialization of a Vue instance tag until the Vue instance is ready.

<template>
  <div>
    <div v-cloak v-if="isShow" ref="dom">{{message}}</div>
  </div>
</template>

<script>
export default {
  data() {
    return {
      isShow: false,
      message: "DOM渲染完成"
    }
  },
  mounted() {
    this.isShow = true;
    const dom = this.$refs.dom;
    if (dom === null) {
      console.log("DOM值为null");
    }
  }
}
</script>

In the above code, we use the v-cloak directive and the v-if directive at the same time to control the rendering and hiding of DOM elements. After the DOM is rendered, get the value of the DOM element and make a judgment.

Summary

Getting the DOM value to null is a common problem in Vue development. This article introduces three methods to obtain the DOM value of null using this.$nextTick(), v-if directive and v-cloak directive. situation, and corresponding code examples are provided. Developers can choose one or more methods based on the specific situation to better handle such problems.

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