Defining Custom Block Nodes

Previous: Adding Event Handlers

Defining Custom Block Nodes

In our previous example, we started with a paragraph, but we never actually told Slate anything about the paragraph block type. We just let it use its internal default renderer, which uses a plain old <div>.

But that's not all you can do. Slate lets you define any type of custom blocks you want, like block quotes, code blocks, list items, etc.

We'll show you how. Let's start with our app from earlier:

class App extends React.Component {
  state = {
    value: initialValue,
  }

  onChange = ({ value }) => {
    this.setState({ value })
  }

  onKeyDown = (event, editor, next) => {
    if (event.key != '&') return next()
    event.preventDefault()
    editor.insertText('and')
  }

  render() {
    return (
      <Editor
        value={this.state.value}
        onChange={this.onChange}
        onKeyDown={this.onKeyDown}
      />
    )
  }
}

Now let's add "code blocks" to our editor.

The problem is, code blocks won't just be rendered as a plain paragraph, they'll need to be rendered differently. To make that happen, we need to define a "renderer" for code nodes.

Node renderers are just simple React components, like so:

// Define a React component renderer for our code blocks.
function CodeNode(props) {
  return (
    <pre {...props.attributes}>
      <code>{props.children}</code>
    </pre>
  )
}

Pretty simple.

See the props.attributes reference? Slate passes attributes that should be rendered on the top-most element of your blocks, so that you don't have to build them up yourself. You must mix the attributes into your component.

And see that props.children reference? Slate will automatically render all of the children of a block for you, and then pass them to you just like any other React component would, via props.children. That way you don't have to muck around with rendering the proper text nodes or anything like that. You must render the children as the lowest leaf in your component.

Now, let's add that renderer to our Editor:

function CodeNode(props) {
  return (
    <pre {...props.attributes}>
      <code>{props.children}</code>
    </pre>
  )
}

class App extends React.Component {
  state = {
    value: initialValue,
  }

  onChange = ({ value }) => {
    this.setState({ value })
  }

  onKeyDown = (event, editor, next) => {
    if (event.key != '&') return next()
    event.preventDefault()
    editor.insertText('and')
  }

  render() {
    return (
      // Pass in the `renderBlock` prop...
      <Editor
        value={this.state.value}
        onChange={this.onChange}
        onKeyDown={this.onKeyDown}
        renderBlock={this.renderBlock}
      />
    )
  }

  // Add a `renderBlock` method to render a `CodeNode` for code blocks.
  renderBlock = (props, editor, next) => {
    switch (props.node.type) {
      case 'code':
        return <CodeNode {...props} />
      default:
        return next()
    }
  }
}

Okay, but now we'll need a way for the user to actually turn a block into a code block. So let's change our onKeyDown function to add a `control-`` shortcut that does just that:

function CodeNode(props) {
  return (
    <pre {...props.attributes}>
      <code>{props.children}</code>
    </pre>
  )
}

class App extends React.Component {
  state = {
    value: initialValue,
  }

  onChange = ({ value }) => {
    this.setState({ value })
  }

  onKeyDown = (event, editor, next) => {
    // Return with no changes if it's not the "`" key with ctrl pressed.
    if (event.key != '`' || !event.ctrlKey) return next()

    // Prevent the "`" from being inserted by default.
    event.preventDefault()

    // Otherwise, set the currently selected blocks type to "code".
    editor.setBlocks('code')
  }

  render() {
    return (
      <Editor
        value={this.state.value}
        onChange={this.onChange}
        onKeyDown={this.onKeyDown}
        renderBlock={this.renderBlock}
      />
    )
  }

  renderBlock = (props, editor, next) => {
    switch (props.node.type) {
      case 'code':
        return <CodeNode {...props} />
      default:
        return next()
    }
  }
}

Now, if you press `control-`` the block your cursor is in should turn into a code block! Magic!

Note: The Edge browser does not currently support control-... key events (see issue), so this example won't work on it.

But we forgot one thing. When you hit `control-`` again, it should change the code block back into a paragraph. To do that, we'll need to add a bit of logic to change the type we set based on whether any of the currently selected blocks are already a code block:

function CodeNode(props) {
  return (
    <pre {...props.attributes}>
      <code>{props.children}</code>
    </pre>
  )
}

class App extends React.Component {
  state = {
    value: initialValue,
  }

  onChange = ({ value }) => {
    this.setState({ value })
  }

  onKeyDown = (event, editor, next) => {
    if (event.key != '`' || !event.ctrlKey) return next()

    event.preventDefault()

    // Determine whether any of the currently selected blocks are code blocks.
    const isCode = editor.value.blocks.some(block => block.type == 'code')

    // Toggle the block type depending on `isCode`.
    editor.setBlocks(isCode ? 'paragraph' : 'code')
  }

  render() {
    return (
      <Editor
        value={this.state.value}
        onChange={this.onChange}
        onKeyDown={this.onKeyDown}
        renderBlock={this.renderBlock}
      />
    )
  }

  renderBlock = (props, editor, next) => {
    switch (props.node.type) {
      case 'code':
        return <CodeNode {...props} />
      default:
        return next()
    }
  }
}

And there you have it! If you press `control-`` while inside a code block, it should turn back into a paragraph!

Next: Applying Custom Formatting