The nirvana of Vue conditional rendering: detailed explanation of the advantages and disadvantages of v-if, v-show, v-else, v-else-if and case analysis

The nirvana of Vue conditional rendering: detailed explanation of the advantages and disadvantages of v-if, v-show, v-else, v-else-if and case analysis

Introduction:
In Vue development, conditional rendering is a very important feature. Vue provides several commonly used instructions to implement conditional rendering, including v-if, v-show, v-else and v-else-if. These instructions can dynamically insert or remove DOM elements based on whether an expression is true or false. This article will explain in detail the usage, advantages and disadvantages of these instructions, and further analyze them through actual cases.

1. v-if instruction
The v-if instruction is the most commonly used conditional rendering instruction in Vue. It determines whether to render a DOM element based on whether the expression is true or false. When the expression is true, v-if will insert the corresponding DOM element into the page; when the expression is false, v-if will remove the corresponding DOM element from the page. The following is an example of using the v-if directive:

<template>
  <div>
    <p v-if="show">显示文本</p>
  </div>
</template>

<script>
export default {
  data() {
    return {
      show: true
    }
  }
}
</script>

In this example, when show is true, the DOM element that displays the text will be rendered; when show is false, the DOM element will be moved remove.

Advantages and disadvantages of the v-if directive:
Advantages:

1. The v-if directive is suitable for elements that need to frequently switch display states. It will change the display state based on the value of the expression. Perform DOM insertion and removal to improve performance.
2. The v-if directive can be used in conjunction with the v-else and v-else-if directives to implement more complex conditional rendering logic.

Disadvantages:

1. The v-if instruction will destroy and rebuild the DOM when switching, and the performance is relatively low. Therefore, when there are many elements that require frequent switching of display states, it is not appropriate to use the v-if instruction. You can consider using the v-show instruction.

2. v-show instruction
The v-show instruction is similar to the v-if instruction. It can also switch the display state of the element based on the true or false expression. The difference is that the v-show instruction is implemented by modifying the display attribute of the element, rather than directly inserting and removing DOM elements. The following is an example of using the v-show directive:

<template>
  <div>
    <p v-show="show">显示文本</p>
  </div>
</template>

<script>
export default {
  data() {
    return {
      show: true
    }
  }
}
</script>

In this example, when show is true, display: block will be used to display the corresponding DOM element; when show is false, display will be used : none hides the corresponding DOM element.

Advantages and disadvantages of the v-show instruction:
Advantages:

1. The v-show instruction is suitable for elements that need to frequently switch display states. Since it only modifies the display attribute of the element, Higher performance.
2. The v-show directive can be used in conjunction with the v-else directive to implement simple conditional rendering logic.

Disadvantages:

1. The v-show instruction does not support the v-else-if instruction, so using v-show will be cumbersome under complex conditional rendering logic.

3. v-else and v-else-if instructions
The v-else and v-else-if instructions are two supplementary instructions in conditional rendering. They can be used with the v-if or v-show directives to implement more complex conditional rendering logic. The following is an example of using the v-else and v-else-if instructions:

<template>
  <div>
    <p v-if="score < 60">不及格</p>
    <p v-else-if="score >= 60 && score < 80">及格</p>
    <p v-else>优秀</p>
  </div>
</template>

<script>
export default {
  data() {
    return {
      score: 85
    }
  }
}
</script>

In this example, different text will be rendered according to different values ​​of score. When the score is less than 60, "Fail" will be rendered; when the score is greater than or equal to 60 and less than 80, "Pass" will be rendered; in other cases, "Excellent" will be rendered.

Advantages and disadvantages of v-else and v-else-if instructions:
Advantages:

1. v-else and v-else-if instructions can be used in conjunction with the v-if instruction To implement more complex conditional rendering logic, making the code clearer and easier to read.

Disadvantages:

1. The v-else and v-else-if instructions can only be used with the v-if instruction and cannot be used with the v-show instruction.

Case analysis:
The following is a specific case showing the usage scenarios, advantages and disadvantages of v-if, v-show, v-else, and v-else-if instructions:

<template>
  <div>
    <button @click="toggleViewType">切换视图类型</button>
    <div v-if="viewType === 'list'">
      <ul>
        <li v-for="item in list">{{ item }}</li>
      </ul>
    </div>
    <div v-else-if="viewType === 'grid'">
      <div v-for="item in list" class="grid-item">{{ item }}</div>
    </div>
    <div v-else>
      暂无数据
    </div>
    <div v-show="showMoreInfo">
      更多信息
    </div>
  </div>
</template>

<script>
export default {
  data() {
    return {
      list: ['A', 'B', 'C'],
      viewType: 'list',
      showMoreInfo: true
    }
  },
  methods: {
    toggleViewType() {
      this.viewType = this.viewType === 'list' ? 'grid' : 'list';
    }
  }
}
</script>

In this case, different data display methods can be displayed by clicking the button to switch the view type. When the view type is 'list', a ul list will be rendered; when the view type is 'grid', a set of div grids will be rendered; when the view type is empty, "No data yet" will be displayed. At the same time, by controlling the value of showMoreInfo, you can decide whether to render "more information".

Through this case, we can see the flexibility, advantages and disadvantages of using v-if, v-show, v-else-if, and v-else instructions. In actual development, we can choose appropriate instructions to perform conditional rendering operations according to specific situations.

Summary:
Vue’s conditional rendering instructions v-if, v-show, v-else, v-else-if are very commonly used in Vue development. Through detailed explanations and case studies of these instructions, we understand how to use them and their advantages and disadvantages. In actual development, we should choose appropriate instructions based on specific needs to achieve the best rendering effect and user experience.

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