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:

const asciidoctor = require('asciidoctor')()
asciidoctor.Extensions.register(function () {
  this.block(function () {
    const self = this
    self.named('shout')
    self.onContext('paragraph')
    self.process(function (parent, reader) {
      const lines = reader.getLines().map(l => l.toUpperCase())
      return self.createBlock(parent, 'paragraph', lines)
    })
  })
})

const text = `[shout]\
\nSay it loud.\
\nSay it proud.`

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

// <div class="paragraph">
// <p>SAY IT LOUD.
// SAY IT PROUD.</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.

const asciidoctor = require('asciidoctor')()

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

registryA.block(function () {
  const self = this
  self.named('shout')
  self.onContext('paragraph')
  self.process(function (parent, reader) {
    // Transform text to uppercase
    const lines = reader.getLines().map(l => l.toUpperCase())
    return self.createBlock(parent, 'paragraph', lines)
  })
})

registryB.block(function () {
  const self = this
  self.named('shout')
  self.onContext('paragraph')
  self.process(function (parent, reader) {
    // Replace period at end of line with three three exclamation marks
    const lines = reader.getLines().map(l => l.replace(/\.$/g, ' !!!'))
    return self.createBlock(parent, 'paragraph', lines)
  })
})

const text = `[shout]\
\nSay it loud.\
\nSay it proud.`

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

// <div class="paragraph">
// <p>SAY IT LOUD.
// SAY IT PROUD.</p>
// </div>
//
// <div class="paragraph">
// <p>Say it loud !!!
// Say it proud !!!</p>
// </div>

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

registryA
registryB

Both registry have a [shout] block extension registered with a specific implementation.

The first block extension is registered in the registryA and will transform the text to uppercase. The other one is registered in the registryB and will replace . by !!!.