Scripting guide

Sometimes you want to do something special in your templates. Perhaps it’s some fancy formatting or iterating through some content and finding specific information. Bartholomew provides the Rhai scripting language for this.

Rhai is a simple scripting language that has many stylistic similarities to Rust, Go, and Python. The integration with Bartholomew is easy to work with.

The basic

  1. Create a file in scripts/ with the extension .rhai
  2. Put some Rhai code in there
  3. Have the code return the value you care about
  4. Use it in a template.

For example, let’s take a look at the scripts/echo.rhai script. Note that because it is named echo.rhai, it will be accessible inside of templates as echo (just remove the .rhai).

let msg = params[0];

"hello " + msg;

On the first line, we accept the first parameter from the template (params[0]) and assign it to the variable named msg.

Variables are mutable in Rhai.

The second line returns the string "hello" concatenated with the value of msg. That’s all there is to a simple Rhai script.

From a template, we can then use this script like this:

{{ echo "world" }}

When we run the template, we will see:

hello world

A more complicated example.

Let’s take a look at scripts/blogs.rhai, which is called in a template as blogs. This script makes a list of all of the blog posts for the site.

// Param 1 should be `site.pages`
let pages = params[0];

// Loop through them and return all of the page objects that are in
// the blog path. We want the results in an array to preserve ordering.
let blog_pages = [];

// Get each blog post, assigning it to {path: object}.
let keys = pages.keys();
for item in keys {
    if item.index_of("/content/blog/") == 0 {
        // Remove /content and .md
        let path = item.sub_string(8);
        path = path.sub_string(0, path.index_of(".md"));

        // Build an object that has `uri` and `page` keys.
        blog_pages.push(#{
            uri: path,
            page: pages[item],
        });
        //blog_pages[path] = pages[item];
    }
   
}
// Newest to oldest, assuming you put the date in the URI
blog_pages.reverse();

// Return the array of blog pages
blog_pages

Again note that this is one long procedural script that starts by fetching a parameter from the params array, and ends by sending back the output of the last line, blog_pages.

The script returns a more complex data type, so let’s see how this one is used in the content_sidebar.hbs template:

<div class="p-4">
    <h4 class="fst-italic">Recent Posts</h4>
    <ol class="list-unstyled mb-0">
        {{#each (blogs site.pages)}}<li><a href="{{uri}}">{{page.head.title}}</a></li>
        {{/each }}
    </ol>
</div>

The code {{#each (blogs site.pages)}} calls blogs with param[0] set to site.pages. Then the each loops through the results.

The value of this within the #each loop is the object that we created in Rhai:

#{
    uri: "/some/path"
    page: #{head: #{...}, body: "some html" }
}

So <a href="{{uri}}">{{page.head.title}}</a> will use this.uri, and the title from the page object.

That’s how you can use Rhai to add custom formatters to the site.

No site would be complete without quality content, so let’s take a look at the markdown guide which will help you create and format your awesome content.