Using KrakenJS Handlebars Preprocessor to Shrink Your Bundle

Problem: Runtime Handlebars adds weight

When you build a KrakenJS application that uses Handlebars templates, the default setup bundles the full Handlebars runtime library. This adds several kilobytes to the JavaScript payload and means every template is compiled on the client at runtime. For performance‑sensitive sites or when you want a smaller attack surface, that overhead is unnecessary.

Solution: Compile templates at build time

The krakenjs/handlebars plugin hooks into Kraken’s preprocess stage. During kraken build it walks the source tree, compiles each .hbs file into a plain JavaScript function, and injects those functions into the module graph. The resulting bundle contains only the compiled functions; the Handlebars runtime package is omitted entirely.

Worked example: Setting up the plugin

1. Initialize a KrakenJS project (or use an existing one) and add the plugin as a dev dependency:

   # Run in the project root
   npm install --save-dev krakenjs/handlebars
   

2. Register the plugin in kraken.config.js. Here we also register a simple helper that converts a string to upper‑case:

   // kraken.config.js
   module.exports = {
     preprocess: [
       {
         name: 'handlebars',
         options: {
           helpers: {
             toUpperCase: (s) => s.toUpperCase()
           }
         }
       }
     ]
   };
   

3. Create a template file templates/hello.hbs:

   {{toUpperCase name}}!

4. Build the application:

   # Run in the project root
   npx kraken build
   

5. Inspect the generated bundle (typically dist/main.js) for two things:
   • Search for a compiled function exported under a key like templates['hello']. You should see something resembling function anonymous(data,helpers,partials) { ... }.
   • Confirm that the string "handlebars" does not appear in the bundle’s dependency list (e.g., no require('handlebars') or ES import).
6. Optionally, run a quick test to verify the output:

   # Node 12+ required
   node -e "
     const fn = require('./dist/main.js').templates['hello'];
     console.log(fn({ name: 'world' }));
   "
   

   Expected output: WORLD!.

Trade‑offs and limitations

Aspect	Benefit	Limitation
Bundle size	Removes Handlebars runtime (~15‑20 KB per template)	None
Build speed	Incremental builds recompile only changed .hbs files	Initial build may take slightly longer due to compilation step
Helper support	Helpers registered in Kraken config are available to all templates	Runtime helpers that rely on async execution or dynamic registration are not supported
Dynamic templates	Static templates are fully precompiled	If you need to load and compile a template string at runtime (e.g., via Handlebars.compile), you must bundle a separate Handlebars runtime

Because the plugin’s last release predates the newest Handlebars versions, you should verify that any Handlebars syntax you use (e.g., block params, newer helper signatures) works with the preprocessor. Check the compiled output for unexpected errors.

Actionable closing

If your KrakenJS app ships many Handlebars templates and you do not rely on async or dynamically registered helpers, adding the krakenjs/handlebars preprocessor is a straightforward way to trim the bundle and improve load times. After configuring the plugin, run a build, inspect the output for the compiled template functions, and ensure the Handlebars runtime is absent. This verification step guarantees you have realized the size reduction without breaking template rendering.