Use a Vue.js Render Prop!

TLDR; I show that Vue can use JSX to utilize the React pattern of a render prop. Source code here

In Vue, templates are typically how we compose/extend/mix/open source our components. This is contra the experience of React developers who write most of their compiled html in JSX.

Thanks to a similar architecture of using the virtualDOM + createElement API and babel-plugin-transform-vue-js, we can write our Vue components in almost the same way we write React! (Not that we should do this for all components, but it's fun to see design patterns and utilize them).

UPDATE: I'm using render props in https://github.com/educents/vue-autosuggest in the renderSuggestion prop, so go check it out!

Note: this article was originally posted here on the Vue.js Developers blog on 2018/01/15

Render props demo

For demonstration, I will use an example from Use a Render Prop! article by Michael Jackson.

First the SFC:

<template>
  <div id="app">
    <Mouse :render="__render"/>
  </div>
</template>

<script>
import Mouse from "./Mouse.js";
export default {
  name: "app",
  components: {
    Mouse
  },
  methods: {
    __render({ x, y }) {
      return (
        <h1>
          The mouse position is ({x}, {y})
        </h1>
      );
    }
  }
};
</script>
<style>
* {
  margin: 0;
  height: 100%;
  width: 100%;
}
</style>

Here in our parent App.vue, the Mouse component will be our child component. Inside Mouse.js we will call our renderProp function callback inside the render method. I've mixed JSX inside the SFC's methods section as you can't use jsx inside template. Here's our Mouse component:

const Mouse = {
  name: "Mouse",
  props: {
    render: {
      type: Function,
      required: true
    }
  },
  data() {
    return {
      x: 0,
      y: 0
    };
  },
  methods: {
    handleMouseMove(event) {
      this.x = event.clientX;
      this.y = event.clientY;
    }
  },
  render(h) {
    return (
      <div style={{ height: "100%" }} onMousemove={this.handleMouseMove}>
        {this.$props.render(this)}
      </div>
    );
  }
};

export default Mouse;

Yes this is a Vue component, not React. Compared with the React version:

import React from 'react'
import ReactDOM from 'react-dom'
import PropTypes from 'prop-types'

// Instead of using a HOC, we can share code using a
// regular component with a render prop!
class Mouse extends React.Component {
  static propTypes = {
    render: PropTypes.func.isRequired
  }

  state = { x: 0, y: 0 }

  handleMouseMove = (event) => {
    this.setState({
      x: event.clientX,
      y: event.clientY
    })
  }

  render() {
    return (
      <div style={{ height: '100%' }} onMouseMove={this.handleMouseMove}>
        {this.props.render(this.state)}
      </div>
    )
  }
}

const App = React.createClass({
  render() {
    return (
      <div style={{ height: '100%' }}>
        <Mouse render={({ x, y }) => (
          // The render prop gives us the state we need
          // to render whatever we want here.
          <h1>The mouse position is ({x}, {y})</h1>
        )}/>
      </div>
    )
  }
})

ReactDOM.render(<App/>, document.getElementById('app'))

Some differences between the two:

Vue has built in prop type validation.
You can't inline an anonymous function that returns jsx inside a template. I've named the callback __render(A single _ before render also throws a Vue warning). You can reasonably use a simple Vue .js component as the parent to pass in an anonymous function, but alas, we're Vue developers so we can mix our templates with our JSX and be happy about it!
We're passing back this (the Vue instance) instead of the React state, but utilize destructuring all the same to pass back x and y.
The obvious Vue differences such as components are just objects, not javascript classes, there is no "setState" as it converts it's Reactive data properties (the corollary to React's state) to getter/setters using Object.defineProperty.
onMouseMove vs onMousemove 💣

Check it out in codesandbox

Vue Render Prop

So there you go, a fairly similar and transferable component design.

Scoped Slots

Evan You tweet

Vue creator Evan You on render props.

If you were to do "render props" with templates, a similar design would be to use scoped slots and would look something like this:

Check it out in codesandbox

Vue Scoped slots are powerful when using templates.

Some advantages to scoped slots are that:

Custom parent-child template injection without a render function or jsx.
You can specify default content easily. In the above example, I pass in a specified slot, that defines a custom message, but when I don't specify a slot, it will fallback to the default slot. A default slot also gives users of the component a "component api" so that you don't have to guess what you might need to render.
Uses destructuring similar to jsx render callback
Parent content to be rendered with child data is "inline" with the template
You will probably never be able to inline a jsx function in your template (https://github.com/vuejs/vue/issues/7439)

Closing Remarks

Why would I want to use the render prop pattern or JSX? The nice thing about this is that using the render function + JSX is a closer-to-the-compiler alternative and allows fine-grain control over rendering. You won't be able to use custom directives like v-model or v-if. Render props themselves have a lot of benefits, as outlined in this episode of Full stack radio where Adam interviews Kent C. Dodds.

If you're a Vue user, does this type of component composing surprise you? If so, I recommend going and reading the official docs which actually explain JSX and render functions in greater detail.

I love that we can share design principles between frameworks. It gives me warm fuzzy feelings in a cruel, cold world that believes there is a war on frameworks. In 2018, try and find the common ground.

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Use a Vue.js Render Prop!

Render props demo

Scoped Slots

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