Custom tags need to be transformed to JavaScript before the browser can execute them. The Riot compiler is designed to transform Riot tags into JavaScript modules. A compiled Riot tag will look like this:

export default {
  css: `my-tag { color: red; }`, // component css string
  template: function() {}, // internal riot template factory function
  exports: {}, // component events and lifecycle methods
  name: 'my-tag' // component id

Each tag file must contain only one tag definition.

In-browser compilation

The riot+compiler.js bundle lets you compile and execute Riot tags directly in your browser for quick prototypes and tests. You can load Riot tags into your browser by setting a type="riot" attribute on your script tags. For example:

<!-- mount point -->

<!-- <my-tag/> is specified in an external file -->
<script src="path/to/javascript/my-tag.riot" type="riot"></script>

<!-- include riot.js and the compiler -->
<script src=""></script>

<!-- compile and mount -->
(async function main() {
  await riot.compile()


Notice that in this case Riot will internally transform all of the export default expressions to enable better support for browsers that don’t support JavaScript modules yet.

Riot can asynchronously compile all of the external tags included via <script> into the DOM and it will render them via riot.mount.

You might prefer using data-src instead of src on your <script> tags to prevent the browser from automatically prefetching any Riot script tag in order and avoid loading the same resources twice. Riot will automatically fetch and compile your tags via AJAX.

In-browser compilation with inline templates

Your Riot.js components could be also be included directly in your page via <template> tags. For example:

<!-- somewhere in your page -->
<template id="my-tag">
    <p>{ props.message }</p>

The riot+compiler.js bundle exposes the compileFromString and inject methods that combined together, can help you compiling the above component:

const tagString = document.getElementById('my-tag').innerHTML

// get the compiled code
const {code} = riot.compileFromString(tagString)

// create the riot component in runtime
riot.inject(code, 'my-tag', './my-tag.html')



The Compilation phase is asynchronous and it will not block your application rendering. However you should use the browser compilation only for prototyping or for quick experiments.

Pre-compilation has the following benefits:

Riot loaders

Tools like webpack and Rollup are the perfect match to bundle your Riot application tags. For such tools we provide Riot official loaders to natively import riot components into your source code:

With the Riot loaders your application entry script might look like this:

import { component } from 'riot'
import MyTag from './path/to/tags/my-tag.riot'


Compilation via Node

import {compile} from '@riotjs/compiler'

const { code, map } = compile('<p>{hello}</p>', {
  file: 'my/path/to/my-component.riot',
  // transform the `:host` css rules
  scopedCss: true,
  // expressions delimiters
  brackets: ['{', '}'],
  // keep HTML comments
  comments: false

The compile function takes a string and returns an object containing the code and map keys. You can handle the code generated however you like and use it in your build system.

Remember that the Riot compiler outputs JavaScript modules and you might want to transpile them in your bundle.

Compilation via Riot.js CLI

You can precompile Riot.js files also via the riot executable, which can be installed with NPM as follows:

npm install @riotjs/cli -g


Here is how riot command works:

# compile a file to current folder
riot some.riot

# compile file to target folder
riot some.riot --output some-folder

# compile file to target path
riot some.riot --output some-folder/some.js

# compile all files from source folder to target folder
riot some/folder --output path/to/dist

For more information, type: riot --help

Watch mode

You can watch directories and automatically transform files when they are changed.

# watch for
riot -w src -o dist

Custom extension

You’re free to use any file extension for your tags (instead of default .riot):

riot --extension html

ES6 Config file

You can use a config file to store and easily configure all of your @riotjs/cli options and create your custom parsers:

riot --config riot.config src

The riot riot.config.js file:

export default {
  output: 'tags/dist',
  // sourcemap type
  sourcemap: 'inline',
  // files extension
  extension: 'foo'

If you want to use custom preprocessors in your project you should install @riotjs/cli as a devDependency and run it via npm scripts:

  "scripts": {
    "build": "npx riot -c riot.config src"
  "devDependencies": {
    "@riotjs/cli": "^4.0.0",
    "@riotjs/compiler": "^4.0.0",
    "pug": "^2.0.3"

That’s how your riot.config.js file might look like in case you want to use pug as components template engine.

import { registerPreprocessor } from '@riotjs/compiler'
import { render } from 'pug'

// register the pug preprocessor
registerPreprocessor('template', 'pug', (code, options) => {
  const { file } = options

  return {
    code: render(code, {
      filename: file,
      pretty: true,
      doctype: 'html'

export default {
  extension: 'pug',

  // assign the pug preprocessor to the riot compiler options
  riot: {
    template: 'pug'

Build your whole application

You can also use the CLI to bundle your entire application.

The app.js file:

import {component} from 'riot'
import App from './app.riot'

riot app.js -o dist/app.js

Your dist/app.js file will contain all the Riot.js components imported in your application and the code to run it.


You can pre-process your components’ contents using your favorite programming language.

The @riotjs/compiler gives you the possibility to register your preprocessors:

import { registerPreprocessor } from '@riotjs/compiler'
import pug from 'pug'
import sass from 'node-sass'
import ts from 'typescript'

registerPreprocessor('template', 'pug', function(code, { options }) {
  const { file } = options
  console.log('Preprocess the template', file)

  return {
    code: pug.render(code),
    // no sourcemap here
    map: null

registerPreprocessor('css', 'sass', function(code, { options }) {
  const { file } = options

  console.log('Compile the sass code in', file)

  const {css} = sass.renderSync({
    data: code

  return {
    code: css.toString(),
    map: null

registerPreprocessor('javascript', 'ts', function(code, { options }) {
  const { file } = options

  const result = ts.transpileModule(code, {
    fileName: file,
    compilerOptions: {
      module: ts.ModuleKind.ESNext

  return {
    code: result.outputText,
    map: null

The Riot.js preprocessors can be only of three types: template, css, javascript (the first argument of the registerPreprocessor function). To compile your components with a different template engine you will need to specify the template option via compiler:

import { compile } from '@riotjs/compiler'

compile(source, {
  template: 'pug'

For the css and javascript preprocessors you can simply enable them directly in your components via type="{preprocessor}" attribute


  <style type="scss">
    import 'color/vars'

    p {
      color: $primary;

  <script type="ts">
    export default {
      getMessage():string {
        return 'hello world'

Pre-processors Caveats

The Riot.js compiler generates sourcempas out of the code provided by the pre-processors. If your preprocessor will not provide any map output the compiler will not output proper sourcemaps.

import { registerPreprocessor } from '@riotjs/compiler'
import babel from '@babel/core'

registerPreprocessor('javascript', 'babel', function(code, { options }) {
  // the babel.transform returns properly an object containing the keys {map, code}
  return babel.transform(code, {
    sourceMaps: true,
    // notice that whitelines should be preserved
    retainLines: true,
    sourceFileName: options.file,
    presets: [[
        targets: {
          edge: true
        loose: true,
        modules: false,
        useBuiltIns: 'usage'

registerPreprocessor('javascript', 'my-js-preprocessor', function(code, { options }) {
  // the Riot.js compiler will not be able to generate sourcemaps
  return {
    code: myPreprocessor(code),
    map: null

The JavaScript preprocessors should preserve the code whitelines of the original source code. Otherwise the resulting sourcemap will have a broken offset.


Similar to the preprocessor, the compiler output can be modified via registerPostprocessor:

import { registerPostprocessor } from '@riotjs/compiler'
import buble from 'buble'

// your compiler output will pass from here
registerPostprocessor(function(code, { options }) {
  const { file } = options
  console.log('your file path is:', file)

  // notice that buble.transform returns {code, map}
  return buble.transform(code)

In this case we make sure that the output code will be converted to es2015 via buble.

Compilation via Riot.js Online Compiler

Finally, you can also compile a tag online

Riot.js Online Compiler