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Creating Neutrino Middleware and Presets

Creating Neutrino middleware and presets can solve a number of use cases in a manner which captures all the necessary configuration and dependencies necessary to accomplish those use cases:

  • You find yourself needing to make the same modifications to all the projects you work on.
  • Your team wants to adopt a managed set of linting rules across projects.
  • You want to add functionality to the build pipeline that has not yet been encapsulated by an existing preset.
  • You want to support building for more platforms than existing presets support.

Getting Started

Neutrino middleware are Node.js modules or packages that export a middleware function. We call these Neutrino middleware because they sit in the middle of Neutrino and webpack, modifying a configuration with each subsequent middleware call. When using these middleware functions, you can use the Neutrino instance provided to the function to modify the configuration, provide your own configuration, expose custom options for your middleware, and execute custom functionality.

Neutrino presets are just Neutrino middleware that encapsulate a specific project need or the combination of other middleware. At a bare minimum, let's start by exporting a middleware function for an empty Neutrino preset:

module.exports = neutrino => {
  // ...

If you are using Babel or Neutrino to build your preset (very meta) with ES modules:

export default neutrino => {
  // ...


The Neutrino instance provided to your middleware function has a config property that is an instance of webpack-chain. We won't go in-depth of all the configuration possibilities here, but encourage you to check out the documentation for webpack-chain for instructions on your particular use cases.

This neutrino.config is an accumulation of all configuration set up to this moment. All Neutrino presets and middleware interact with and make changes through this config, which is all available to your preset.

Including and merging other middleware

If your preset depends on other Neutrino presets and/or middleware, or you are creating a preset that is a combination of multiple presets and/or middleware, you can install them as dependencies and simply have Neutrino use them as middleware. When users install your preset, they will bring along these dependencies defined with your package without needing to to include your extended presets in their own commands.

Example: Define a Neutrino preset which combines Node.js and Mocha presets.

const node = require('@neutrinojs/node');
const mocha = require('@neutrinojs/mocha');

module.exports = neutrino => {

  // neutrino.config now contains the accumulation of configuration from
  // the Node.js and Mocha presets

Sample Preset: JavaScript Standard Style

Let's create a preset from scratch which allows users to augment their project with JavaScript Standard Style. For this sample preset we are using Yarn for managing dependencies, but you may use the npm client if you desire.

Important: this preset is not meant to be functional; rather it is used to demonstrate the concepts of creating presets.

# Create a new directory for your project and change into it:
mkdir neutrino-preset-standard-style && cd neutrino-preset-standard-style

# Initialize your project with a package.json:
yarn init --yes

# Install the dependencies needed by our preset
yarn add standard-loader standard

# Create the main file to the preset, e.g. index.js
touch index.js

Let's edit this index.js file to add our preset:

module.exports = neutrino => {
      .test(neutrino.regexFromExtensions(['js', 'jsx']))
        .options({ snazzy: false });

Middleware Options

If you want to expose custom options for your middleware that are not appropriate to be stored in the Neutrino config, your package can use a closure for the options, and return a middleware function. You may then document to users how they can go about affecting how your middleware works by manipulating these options via their own middleware or .neutrinorc.js. You can then merge these options back with your defaults within your middleware when needed. This is how Neutrino's own core middleware works.


module.exports = (opts = {}) => (neutrino) => {
  const options = {
    quiet: false,
    logLevel: 'warn',

  // ...

Working with paths

When working with paths, remember that your preset will be running in the context of a project. You should take care to define application paths by referencing the current working directory with process.cwd(). For example, if you wanted to interact with a file with a project, you would merge the path via path.join(process.cwd(), 'project.file').

Neutrino provides a number of paths that have been defaulted through neutrino.options or configured by the user. Please consider using these paths for your preset so they play nice with others.

Modifying Neutrino options

If you wish to modify Neutrino options, including paths, be aware that other middleware may have been loaded before or after your own middleware, which may have unintended consequences. If possible, document recommended Neutrino option changes to your middleware consumers for them to change manually in their .neutrinorc.js. See the Neutrino API for a list of options you can manipulate.

Loader and Babel modules

Because of package conflicts or unknown layout of a project's node_modules directory, it is usually safer to define loaders, Babel plugins, and Babel presets to webpack absolutely than by name. In our sample preset above, while we could have passed the loader as just 'standard-loader', it is safer to resolve its location relative to our preset than having webpack et al attempt to load it later from a different, potentially incorrect location. Instead we passed require.resolve('standard-loader').

As a rule of thumb, if your preset is the one using require, you are safe to require by name. If you are passing the name of the module off to be required by webpack or Babel, instead pass the path to the module via require.resolve.


When your preset is ready to be used by others, feel free to publish and distribute! By putting your preset on npm, GitHub, or another location, you can share the hard work put into abstracting away configuration and save everyone in the community time and effort. As long as the Neutrino CLI or another preset can require your preset, it puts no restrictions on where you want to host it.