If Reptar is missing some functionality you desire then you can further customize Reptar through the use of middleware.

Middleware is a function that is given the current reptar instance, allowing you to access any APIs on the Reptar object and manipulate it however you want.

Middleware is ran in-between the update and build step of reptar build.

You add middleware through the reptar.config.js file.

module.exports = {
  // Reptar iterates through each middleware function in order defined.
  middlewares: [

    // Reptar attempts to load an npm package named 'my-middleware'

    // Reptar uses the middleware function directly.


Let's say you wanted to add a custom frontmatter value to every File object. You wanted to take the title of the File and make it all lower case.

// All within reptar.config.js

function toLowerCaseMiddleware(reptar) {
  for (const fileKey in reptar.destination) {
    const file = reptar.destination[fileKey];

    file.data.titleLower = file.data.title.toLowerCase();

module.exports = {
  middlewares: [

And now you will have a titleLower variable available in every rendered file.

Lifecycle Middleware

Reptar also has support for middleware to be ran at certain points in the build lifecycle.

You can configure the lifecycle middleware in your reptar.config.js file.

module.exports = {
  // The value of every lifecycle middleware is the same as regular middleware.
  lifecycle: {
    // This is ran right before Reptar updates itself from the filesystem.
    willUpdate: [],

    // This is ran right after Reptar updates itself from the filesystem.
    didUpdate: [],

    // This is ran right before Reptar is going to build your site.
    willBuild: [],

    // This is ran right after Reptar built your site.
    didBuild: [],

Asynchronous Middleware

Middleware functions can also be asynchronous.

To opt-in to asynchronous behavior you can:

  1. Return a Promise.
function promiseMiddleware(reptar) {
  return new Promise((resolve) => {
    setTimeout(() => {
    }, 100);
  1. Add a second argument to your middleware function, called done, and call it when you're done.
function doneMiddleare(reptar, done) {
  setTimeout(() => {
  }, 100);

Current Reptar Middleware

Add excerpt data to each File object. Useful when rendering a list of pages.

Minify your rendered files.