Render Function API

breaking

Overview

This change will not affect <template> users.

Here is a quick summary of what has changed:

• h is now globally imported instead of passed to render functions as an argument
• render function arguments changed to be more consistent between stateful and functional components
• VNodes now have a flat props structure

For more information, read on!

Render Function Argument

2.x Syntax

In 2.x, the render function would automatically receive the h function (which is a conventional alias for createElement) as an argument:

// Vue 2 Render Function Example
export default {
  render(h) {
    return h('div')
  }
}

3.x Syntax

In 3.x, h is now globally imported instead of being automatically passed as an argument.

// Vue 3 Render Function Example
import { h } from 'vue'

export default {
  render() {
    return h('div')
  }
}

VNode Props Format

2.x Syntax

In 2.x, domProps contained a nested list within the VNode props:

// 2.x
{
  staticClass: 'button',
  class: {'is-outlined': isOutlined },
  staticStyle: { color: '#34495E' },
  style: { backgroundColor: buttonColor },
  attrs: { id: 'submit' },
  domProps: { innerHTML: '' },
  on: { click: submitForm },
  key: 'submit-button'
}

3.x Syntax

In 3.x, the entire VNode props structure is flattened. Using the example from above, here is what it would look like now.

// 3.x Syntax
{
  class: ['button', { 'is-outlined': isOutlined }],
  style: [{ color: '#34495E' }, { backgroundColor: buttonColor }],
  id: 'submit',
  innerHTML: '',
  onClick: submitForm,
  key: 'submit-button'
}

Registered Component

2.x Syntax

In 2.x, when a component has been registered, the render function would work well when passing the component's name as a string to the first argument:

// 2.x
Vue.component('button-counter', {
  data() {
    return {
      count: 0
    }
  }
  template: `
    <button @click="count++">
      Clicked {{ count }} times.
    </button>
  `
})

export default {
  render(h) {
    return h('button-counter')
  }
}

3.x Syntax

In 3.x, with VNodes being context-free, we can no longer use a string ID to implicitly lookup registered components. Instead, we need to use an imported resolveComponent method:

// 3.x
import { h, resolveComponent } from 'vue'

export default {
  setup() {
    const ButtonCounter = resolveComponent('button-counter')
    return () => h(ButtonCounter)
  }
}

For more information, see The Render Function Api Change RFC.

Migration Strategy

Migration build flag: RENDER_FUNCTION

Library Authors

h being globally imported means that any library that contains Vue components will include import { h } from 'vue' somewhere. As a result, this creates a bit of overhead since it requires library authors to properly configure the externalization of Vue in their build setup:

• Vue should not be bundled into the library
• For module builds, the import should be left alone and be handled by the end user bundler
• For UMD / browser builds, it should try the global Vue.h first and fallback to require calls

Next Steps

See Render Function Guide for more detailed documentation!