Custom

New in v1.0.0

Eleventy now allows the addition of custom template extensions, meaning that you can use Eleventy to process any arbitrary file extension and compile it to your site’s output folder.

Introductory Example: *.clowd #

clowd is a pretend templating language that we’ve just created. It uses the .clowd file extension. The purpose of the language is to translate any occurrences of the word cloud to the word butt instead.

module.exports = function(eleventyConfig) {
  // Add as a valid extension to process
  // Alternatively, add this to the list of formats you pass to the `--formats` CLI argument
  eleventyConfig.addTemplateFormats("clowd");

  // "clowd" here means that the extension will apply to any .clowd file
  eleventyConfig.addExtension("clowd", {
    compile: async (inputContent) => {
      // Replace any instances of cloud with butt
      let output = inputContent.replace(/cloud/gi, "butt");

      return async () => {
        return output;
      };
    }
  });
};

Example: Add Sass support to Eleventy #

For a more realistic sample, here’s an example of Eleventy looking for all .sass files in a project’s input directory to process them to your output directory.

// Don’t forget to `npm install sass`!
const sass = require("sass");

module.exports = function(eleventyConfig) {
  eleventyConfig.addTemplateFormats("scss");

  // Creates the extension for use
  eleventyConfig.addExtension("scss", {
    outputFileExtension: "css", // optional, default: "html"

    // `compile` is called once per .scss file in the input directory
    compile: async function(inputContent) {
      let result = sass.compileString(inputContent);

      // This is the render function, `data` is the full data cascade
      return async (data) => {
        return result.css;
      };
    }
  });
};

We’re using compileString from the Sass library above for speed benefits over their asynchronous counterparts (reported by the Sass documentation).

Note also that the data is not used in the above example. This is the full Eleventy data cascade and may be more useful in other templating languages.

The above extension would process a file located at subdir/test.scss to the output directory at _site/subdir/test.css.

Using inputPath #

You can pass in both the file’s inputPath and the Eleventy includes folder to provide a set of directories to look for when using Sass’ @use, @forward, and @import features. Read more about loadPaths on the Sass documentation.

const sass = require("sass");
const path = require("node:path");

module.exports = function(eleventyConfig) {
   // add as a valid template language to process, e.g. this adds to --formats
  eleventyConfig.addTemplateFormats("scss");

  eleventyConfig.addExtension("scss", {
    outputFileExtension: "css", // optional, default: "html"

    // can be an async function
    compile: function (inputContent, inputPath) {
      let parsed = path.parse(inputPath);

      let result = sass.compileString(inputContent, {
        loadPaths: [
          parsed.dir || ".",
          this.config.dir.includes
        ]
      });

      return (data) => {
        return result.css;
      };
    }
  });
};

Skipping a template from inside of the compile function #

To add support for Sass’ underscore convention (file names that start with an underscore aren’t written to the output directory), just return early in the compile function (don’t return a render function).

    // some configuration truncated …
    compile: async function (inputContent, inputPath) {
      let parsed = path.parse(inputPath);
      if(parsed.name.startsWith("_")) {
        return;
      }

      let result = sass.compileString(inputContent);

      return async (data) => {
        return result.css;
      };
    }

This functionality is more-or-less identical to the compileOptions permalink: false overrides, documented later on this page.

Overriding an Existing Template Language #

You can override existing template languages too! (Thank you to Ben Holmes of Slinkity for this contribution).

In these example, we switch from the Eleventy default markdown-it to marked for markdown processing.

const { marked } = require("marked");

module.exports = function(eleventyConfig) {
  eleventyConfig.addExtension("md", {
    compile: function (inputContent, inputPath) {
      let html = marked.parse(inputContent);

      return function (data) {
        // Example: use `marked` only if useMarked is set in the Data Cascade
        if(data.useMarked) {
          return html;
        }

        // You can also access the default `markdown-it` renderer here:
        return this.defaultRenderer(data);
      };
    }
  });
};

Note that overriding md opts-out of the default pre-processing by another template language Markdown Files. As mentioned elsewhere, improvements to add additional hooks for preprocessing will likely come later.

Full Options List #

compile #

• Required for new file extensions. Optional for extension overrides.

compile is an async-friendly function that takes two parameters:

• inputContent: the full content of the file to parse (as a string).
• inputPath: the path to the file (as a string, useful for looking up relative imports)

compile can return:

• nothing (undefined) to indicate that the file should be ignored and not used as a page
• a render function (also async-friendly)

  compile: async (inputContent, inputPath) => {
    return async () => {
      return inputContent;
    };
  }

The render function is passed the merged data object (i.e. the full Data Cascade available inside templates). The render function returned from compile is called once per output file generated (one for basic templates and more for paginated templates).

outputFileExtension #

• Optional: Defaults to html

When the output file is written to the file system, what file extension should be used?

init #

• Optional

An async-friendly function that runs once (no matter how many files use the extension) for any additional setup at the beginning before any compilation or rendering.

{
  init: async function() {
    // has access to current configuration settings in `this.config`
  },
}

read #

• Optional: Defaults to true

Set to false to opt out of reading the contents of files from the file system. This is useful if you’re using an external bundler to read the files (e.g. the Vue plugin uses rollup to read and compile .vue files).

{
  read: false,
}

Use with compileOptions.setCacheKey to get more fine-grained control over how the template is cached.

isIncrementalMatch #

Docs coming soon

getData and getInstanceFromInputPath #

• Optional

Controls if and how additional data should be retrieved from a JavaScript object to populate the Data Cascade. If your templates aren’t compiling JavaScript objects, you probably won’t need this.

Notably, this is separate from (in addition to) front matter parsing (which requires read: true). As an example, this is used by the Vue plugin to retrieve the return from the Vue data() function in the Vue component to feed back into the Data Cascade.

{
  // this is the default
  getData: false // no additional data is used
}

{
  getData: async function(inputPath) {
    // DIY, this object will be merged into data cascade
    return {};
  },
}

{
  // get the `data` property from the instance.
  getData: ["data"],
  // * `getData: true` is aliased to ["data"]
  // * You can use more than one property name! ["data", "otherPropName"]

  getInstanceFromInputPath: function(inputPath) {
    // Return the JavaScript object from which the `data` property will be retrieved.
    let instance = doSomethingMyselfToFetchAJavaScriptObject(inputPath);
    return instance;
  }
}

{
  // if getData is `false`, `eleventyDataKey` will not be used.
  getData: true,

  getInstanceFromInputPath: function(inputPath) {
    return {
      // Overrides `getData` for this instance
      eleventyDataKey: ["myOverrideData"],

      // Will not be used
      data: {
        notAvailableOnGlobalData: 456
      },

      // Will be used.
      myOverrideData: {
        availableOnGlobalData: 123
      }
    }
  }
}

compileOptions #

compileOptions.permalink to Override Permalink Compilation #

• Optional

This has the same signature as the compile function and expects a reusable render function to be returned.

{
  compileOptions: {
    permalink: function(contents, inputPath) {
      return (data) => {
        // Return a string to override: you’ll want to use `data.page`
        // Or `return;` (return undefined) to fallback to default behavior
      }
    }
  }
}

• Don’t compile permalink strings in the parent template language
  • permalink: "raw"
• Don’t write any files to the file system:
  • permalink: false
  • permalink: (contents, inputPath) => false
  • permalink: (contents, inputPath) => ((data) => false)
• Override the default permalink function (return a string to override)
  • permalink: (contents, inputPath) => "…"
  • permalink: (contents, inputPath) => ((data) => "…") (use the data cascade)
  • If you return nothing (or undefined), this will revert to the default permalink behavior.

This provides another way to implement Sass’ underscore convention to skip writing the file to the output directory:

// … some configuration truncated

{
  compileOptions: {
    permalink: function(contents, inputPath) {
      let parsed = path.parse(inputPath);
      if(parsed.name.startsWith("_")) {
        return false;
      }
    }
  }
}

compileOptions.spiderJavaScriptDependencies #

• Optional: Defaults to false

Enable to use Eleventy to spider and watch files require’d in these templates. This allows you to control the Watch JavaScript Dependencies feature on a per-template language basis. Most template languages will want the default here and keep this feature disabled.

compileOptions.cache for advanced control of caching #

• Optional: Defaults to the value of read

This controls caching for the compilation step, which saves the compiled template function for reuse if another template attempts to compile with the same key (usually a file’s contents).

By default, whether or not cache is enabled is tied to boolean value of read. If read: true, then cache will also be true. It’s unlikely you will need this, but you can override this to mismatch read.

You can also control the caching key using getCacheKey. It might be useful to change this when using read: false and contents are unavailable.

{
  read: false,
  compileOptions: {
    cache: true,
    getCacheKey: function(contents, inputPath) {
      // return contents; // this is the default
      return inputPath; // override to cache by inputPath (this means the compile function will not get called when the file contents change)
    }
  }
}

Other pages in Template Languages:

• HTML
• Markdown
• JavaScript
• Nunjucks
• Liquid
• Handlebars
• Mustache
• EJS
• HAML
• Pug
• Custom