Register Extensions

These extension points are currently available.

Preprocessor: Processes the raw source lines before they are passed to the parser. See Preprocessor Example.
Tree processor: Processes the Asciidoctor.Document (AST) once parsing is complete. See Tree Processor Example.
Postprocessor: Processes the output after the document has been converted, but before it’s written to disk. See Postprocessor Example.
Docinfo Processor: Adds additional content to the header or footer regions of the generated document. See Docinfo Processor Example.
Block processor: Processes a block of content marked with a custom block style (i.e., [custom]). (similar to an AsciiDoc filter) See Block Processor Example.
Block macro processor: Registers a custom block macro and processes it (e.g., gist::12345[]). See Block Macro Processor Example.
Inline macro processor: Registers a custom inline macro and processes it (e.g., Save). See Inline Macro Processor Example.
Include processor: Processes the include::<filename>[] directive. See Include Processor Example.

Register one or more extensions

You can register an extension globally as follows:

import { Extensions, convert } from '@asciidoctor/core'

Extensions.register(function () {
  this.block(function () {
    const self = this
    self.named('callout')
    self.onContext('paragraph')
    self.process(function (parent, reader) {
      const lines = reader.getLines()
      return self.createBlock(parent, 'paragraph', lines, { role: 'callout' })
    })
  })
})

const text = `[callout]
Deploy to production only after all tests pass.`

const html = await convert(text)
console.log(html)

// <div class="paragraph callout">
// <p>Deploy to production only after all tests pass.</p>
// </div>

You can register more than one processor of each type, though you can only have one processor per custom block or macro. Each registered class is instantiated when the Asciidoctor.Document is created.

There is currently no extension point for processing a built-in block, such as a normal paragraph. Look for that feature in a future Asciidoctor release.

You can also create one or more registries. It can be useful when you want to convert the same text with different extensions enabled.

import { Extensions, convert } from '@asciidoctor/core'

const registryA = Extensions.create()
const registryB = Extensions.create()

registryA.block(function () {
  const self = this
  self.named('callout')
  self.onContext('paragraph')
  self.process(function (parent, reader) {
    // Render as a paragraph with a CSS role
    const lines = reader.getLines()
    return self.createBlock(parent, 'paragraph', lines, { role: 'callout' })
  })
})

registryB.block(function () {
  const self = this
  self.named('callout')
  self.onContext('paragraph')
  self.process(function (parent, reader) {
    // Render as a semantic <aside> element
    const lines = reader.getLines()
    const html = `<aside class="callout">${lines.join('\n')}</aside>`
    return self.createBlock(parent, 'pass', html)
  })
})

const text = `[callout]
Deploy to production only after all tests pass.`

console.log(await convert(text, { extension_registry: registryA }))
console.log('')
console.log(await convert(text, { extension_registry: registryB }))

// <div class="paragraph callout">
// <p>Deploy to production only after all tests pass.</p>
// </div>
//
// <aside class="callout">Deploy to production only after all tests pass.</aside>

In the example above, we’ve created two registries:

registryA
registryB

Both registries have a [callout] block extension registered with a specific implementation.

The first block extension is registered in registryA and renders the content as a paragraph with a callout CSS role. The other is registered in registryB and wraps the content in a semantic <aside> element.