The secret weapon of Vue conditional rendering: detailed explanation of the usage and effect comparison of v-if, v-show, v-else, v-else-if

The secret weapon of Vue conditional rendering: detailed explanation of the usage and effect comparison of v-if, v-show, v-else, v-else-if

Vue as A popular front-end framework that provides us with a wealth of tools and instructions to control the display and hiding of views. In Vue, conditional rendering is a common operation that is used to decide whether to show or hide elements based on different conditions. In this article, we will discuss the conditional rendering instructions in Vue in detail: v-if, v-show, v-else, v-else-if, and compare their usage and effects. At the same time, we will provide specific code examples to help readers better understand the application scenarios of these instructions.

1. v-if directive
   The v-if directive is one of the most commonly used conditional rendering directives in Vue. It decides whether to render an element based on specified conditions. When the condition is true, the element will be rendered into the DOM, otherwise it will be removed from the DOM. The v-if instruction has high switching overhead and will recreate or destroy elements when conditions change.

The following is an example of using the v-if directive:

<template>
  <div>
    <p v-if="isShow">这是一个使用v-if指令的示例</p>
  </div>
</template>

<script>
export default {
  data() {
    return {
      isShow: true,
    };
  },
};
</script>

In the above example, when isShow is true, the paragraph element will be rendered into the DOM; when isShow When false, the paragraph element will be removed from the DOM.

2. v-show instruction
   The v-show instruction is similar to the v-if instruction, both are used for conditional rendering, but there are some differences between the two. The v-show instruction controls the display and hiding of elements by modifying the CSS display attribute of the element. When the condition is true, the element is shown; when the condition is false, the element is hidden. Different from v-if, the v-show instruction has less switching overhead. It only changes the display attribute of the element and does not actually create or destroy the element.

The following is an example of using the v-show directive:

<template>
  <div>
    <p v-show="isShow">这是一个使用v-show指令的示例</p>
  </div>
</template>

<script>
export default {
  data() {
    return {
      isShow: true,
    };
  },
};
</script>

In the above example, when isShow is true, the paragraph element will be displayed; when isShow is false, The paragraph element will be hidden.

3. v-else command
   The v-else command is used in conjunction with the v-if or v-show command. It means that the current element is the "negation" of the previous element. The v-else directive must follow the v-if or v-show directive and cannot have any parameters or expressions.

The following is an example of using the v-else directive:

<template>
  <div>
    <p v-if="isShow">这是一个使用v-if指令的示例</p>
    <p v-else>这是一个使用v-else指令的示例</p>
  </div>
</template>

<script>
export default {
  data() {
    return {
      isShow: true,
    };
  },
};
</script>

In the above example, when isShow is true, the first paragraph element will be rendered into the DOM ;When isShow is false, the second paragraph element will be rendered into the DOM.

4. v-else-if command
   The v-else-if command is used in conjunction with the v-if or v-show command. It means that the current element is the "negation of the previous element and the affirmation of another condition". The v-else-if directive must follow the v-if or v-show directive and can have one parameter or expression.

The following is an example of using the v-else-if directive:

<template>
  <div>
    <p v-if="type === 'A'">这是类型A的示例</p>
    <p v-else-if="type === 'B'">这是类型B的示例</p>
    <p v-else>这是其他类型的示例</p>
  </div>
</template>

<script>
export default {
  data() {
    return {
      type: 'A',
    };
  },
};
</script>

In the above example, depending on the different values ​​of type, different paragraph elements will be rendered to the DOM. middle. When type is 'A', the first paragraph element will be rendered; when type is 'B', the second paragraph element will be rendered; when type is other values, the third paragraph element will be rendered.

To sum up, v-if, v-show, v-else, v-else-if are commonly used conditional rendering instructions in Vue. They all have their own advantages and applicable scenarios. If you need to frequently switch the display and hiding of elements, and the rendering overhead is relatively small, you can use the v-show instruction; if you need to dynamically create or destroy elements based on different conditions, or the switching overhead is large, you can use the v-if instruction; if If you need to render different elements based on multiple conditions, you can use the v-else-if directive; if you need to render some default elements when the conditions of the v-if or v-show directive are not met, you can use the v-else directive.

I hope that through the introduction of this article, readers can better understand and apply the conditional rendering instructions in Vue, and choose the appropriate instructions to control the display and hiding of views according to specific needs.

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