What should I do if the default value of vue slot is missing?

In Vue, slot is a very powerful function. It allows us to define some "vacancies" in the parent component, and then fill in the "content" in the child component to implement the function of the composite component. But sometimes, we encounter a problem: when we set a default value for the slot in the parent component, the default value disappears. In this case, what should we do? Let me introduce to you the solution to this problem.

First, let’s take a look at how this problem arises. When we set the default value for the slot in the parent component, we can use the following code:

<!-- 父组件 -->
<template>
  <div>
    <slot>默认值</slot>
  </div>
</template>

This code indicates that if the child component does not fill the slot, the "default value" will be displayed. Then let's take a look at the code of the subcomponent:

<!-- 子组件 -->
<template>
  <div>
    <slot></slot>
  </div>
</template>

This code indicates that this subcomponent does not fill the slot, so the default value of the parent component will be used. But here’s the problem – even if we don’t fill the slot in the child component, its default value is gone!

This is because Vue will give priority to the content filled in the subcomponent when processing the slot. In other words, when the slot is not filled, Vue will treat the default value of the slot as an element in the parent component and then place it in the child component. This behavior may cause some problems in our program, especially in complex components, the problem may be more complicated.

So, how do we solve this problem? In fact, it is very simple. You only need to add a useless label in the subcomponent, such as the following code:

<!-- 子组件 -->
<template>
  <div>
    <slot>
      <span></span>
    </slot>
  </div>
</template>

This code shows that even if the slot is not filled in the subcomponent, Vue will empty it. The span tag is treated as the content filled by the child component, so that the default value in the parent component will not be overwritten.

Of course, in actual development, we may use more complex tags to fill slots to achieve better display effects. But no matter what, we need to ensure that no unexpected situations will occur if the slot is not filled. Therefore, the above method can be used as a reference to help everyone avoid problems when using slots.

To summarize, this article mainly explains the problem of missing default values ​​when using slots in Vue. Due to the behavior of Vue handling slots, unexpected results may occur in subcomponents, so we need to add a useless tag to the subcomponent to avoid this problem. I hope the above content can help you make better use of the slot function in Vue and implement better components.

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