A processor is a function to transform the content of pages and assets. Let's see an example of a processor to minify HTML pages:

function minifyHTML(page) {
  page.content = minify(page.content);

If you want to use this processor to build your site, you can register it in the _config.js file:

site.process([".html"], minifyHTML);

Now, all HTML pages with be minified.

Access to page data

As you can see in the previous example, the function receives an object with the page (or asset). This means that you can access not only to the page content but to many other data:

function process(page) {
  page.content; // The content of the page
  page.document; // The parsed HTML code, to use the DOM API
  page.src; // The info about the source file of this page
  page.dest; // The info about the destination of the page; // All data available for this page (frontmatter merged with _data)

For example, let's say you only want to minify the pages with the value minify as true:

function minifyHTML(page) {
  if ( {
    page.content = minify(page.content);

Note that you can use the DOM API with methods like querySelector, setAttribute, etc to modify HTML code. For example, let's create a processor to add automatically the alt attribute to all images:

function altAttribute(page) {
  page.document.querySelectorAll("img").forEach((img) => {
    if (!img.hasAttribute("alt")) {
      img.setAttribute("alt", "This is a random alt");

Note: processors are executed just after render the page (with a template engine).

Process assets

Note that processors only can transform pages or assets that are previously loaded. So if you want to process some assets (like CSS or JavaScript files), make sure that they are loaded before. See Loaders for more information about how to register a new loader. Let's see an example of how to load and transform JavaScript files:

import lume from "lume/mod.ts";
import textLoader from "lume/loaders/text.ts";

const site = lume();

// Load JavaScript files as plain text:
site.loadAssets([".js"], textLoader);

// Process the JavaScript files
site.process([".js"], function (page) {
  page.content = myBundler(page.content);

  page.dest.path += ".min"; // Append .min to the filename, so it will be saved as example.min.js


If you need to execute a function before rendering (for example, to configure a custom template engine or add extra data to some pages), you can use a preprocessor. Preprocessors work like processors but with two differences.

Let's create a preprocessor to include a variable with the source filename:

  (page) => = page.src.path + page.src.ext,