5. Webpack loaders#

In the process of "bundling" (creating the static code that gets loaded into the browsers, webpack needs to be instructed on how to handle various types of files. JavaScript/JSX code gets handled by the Babel compiler, etc.

Volto includes several other webpack loaders:

  • .less files are loaded with the LESS Loader, pipelined through PostCSS

  • .css files are loaded directly

  • .svg files, if placed in a folder called icons, can be loaded as React elements

  • the file loader, for static resources such as images

PostCSS is a pluggable framework that enables enhancements and transformations of CSS.

5.1. Add your own Webpack loader#

Sometimes Razzle provides a plugin for your needed loader, which takes care of loading and passing the proper options to that Webpack loader. To load a Razzle plugin, for example, to load the razzle-plugin-scss, you need to export a plugins field in your razzle.config.js or razzle.extend.js.

Here's an example razzle.extend.js that allows an addon to load that plugin. Make sure to add the razzle-plugin-scss as dependency of your addon.

const plugins = (defaultPlugins) => {
  return defaultPlugins.concat(['scss']);

const modify = (config, { target, dev }, webpack) => {
  return config;

module.exports = {

If there's no Razzle plugin, you'll have to write your own Razzle extender plugin that inserts the proper rules. See the Volto LESS Plugin for an example of how to define a new loader, with the Bundle Analyzer as a simpler example for Volto Razzle/Webpack plugins.