在Vue 中，渲染函數(shù)適用於需要動態(tài)選擇標籤、創(chuàng)建透明傳遞屬性的包裝組件或優(yōu)化性能時。 1. 渲染函數(shù)用JavaScript 返回虛擬DOM 節(jié)點，替代模板語法；2. 使用h() 函數(shù)創(chuàng)建VNode，接受標籤名、屬性對象和子節(jié)點；3. 可手動處理插槽內(nèi)容並動態(tài)切換組件；4. 適用於UI 庫組件、過渡包裝或傳送門組件；5. 注意性能並非總是提升，需合理使用避免過度嵌套，並正確傳遞$attrs 和$listeners。

In Vue, a render function gives you more control over how components are generated and rendered. This is especially useful when building advanced or dynamic components where using templates isn't flexible enough. You don't always need them, but when you do — like for higher-order components, dynamic tag selection, or performance-sensitive scenarios — render functions become a powerful tool.

Here's how to use them effectively in real-world Vue component development.

What Is a Render Function and When to Use It?

A render function in Vue is an alternative to writing template markup. Instead of using HTML-like syntax in the <template></template> block, you write JavaScript that returns a virtual DOM node (VNode). Vue uses this VNode tree to update the actual DOM efficiently.

You might reach for a render function when:

• You need to dynamically choose which tag or component to render
• You're creating wrapper components that pass down props/slots transparently
• You want to optimize rendering by avoiding unnecessary abstractions
• You're building reusable logic that manipulates children or slots programmatically

This is different from using h() in JSX or templates — here, you're working closer to the metal, with full access to Vue's rendering system.

How to Write a Basic Render Function

Vue provides the h function (short for hyperscript) to create virtual nodes. Here's a minimal example:

 import { h } from 'vue'

export default {
  render() {
    return h('div', 'Hello, render function!')
  }
}

The h function takes three main arguments:

• Type: HTML tag name ( 'div' ), component ( MyComponent ), or special Vue types like Fragment , Teleport
• Props: An object of attributes, props, listeners ( onClick , etc.)
• Children: A string, array of VNods, or nested h() calls

Example with props and children:

 render() {
  return h(
    'button',
    {
      class: 'btn primary',
      onClick: () => console.log('Clicked')
    },
    'Click me'
  )
}

It looks more verbose than a template at first, but it gives you fine-grained control, especially when things get dynamic.

Using Render Functions with Slots and Dynamic Components

One of the most common advanced uses is handling slots manually inside a render function. This is helpful when you need to wrap or modify slot content before rendering.

 render() {
  const defaultSlot = this.$slots.default ? this.$slots.default() : []
  return h('div', defaultSlot)
}

You can also dynamically switch between tags or components based on props:

 props: ['as'],
render() {
  const Tag = this.as // could be 'div', 'span', or a component
  return h(Tag, this.$attrs, this.$slots.default?.())
}

This pattern is used heavily in UI libraries where components need to be highly customizable — think buttons that accept a tag prop to render as <a></a> , <button></button> , or even a router link.

Also, if you're writing something like a transition wrapper or portal component, render functions let you manipulate what gets rendered without relying on templates.

Performance Considerations and Best Practices

Render functions aren't inherently faster than templates — Vue compiles templates into optimized render functions under the hood. However, when you write your own render function, you can avoid some overhead or unnecessary checks.

Some tips:

• Only use render functions when needed; readability matters
• Use h consistently and keep structure clean
• Avoid deeply nested h() calls unless necessary
• Be careful with $attrs and $listeners — forward them properly
• If you're wrapping components, consider using defineProps and defineSlots in <script setup></script> for clarity

Also, note that not all features work exactly the same in render functions. For instance, v-model , directives, and scoped styles behave differently or require manual handling.

So yes, render functions in Vue are powerful, but they come with a trade-off in readability. Use them when you really need that extra control — especially in utility components, wrappers, or when building design system-level tools. Otherwise, stick with templates or the Composition API for simplicity.

That's pretty much it. Not hard once you get the hang of h() , but easy to overuse.

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