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Custom Helpers

Custom helpers and Lo-Dash mixins are so easy to use with Assemble, the possibilities are truly limitless.

To make it easier for Assemble users to consume custom helpers created by other users, we offer the following conventions and recommendations for your consideration.

Also see Helpers | options.helpers

Registering custom helpers

Helpers can either be an object or a single register function. If register is on the object, then it calls the register function, passing in the engine. Otherwise each method is registered as a helper. For example, the following will result in 2 helpers being registered: = function (str)  {  return  str; }; = function (str)  {  return  str; };

And the following will result in the foo helper getting register directly through Handlebars:

module.exports.register = function (Handlebars, options)  { 
  Handlebars.registerHelper('foo', function (str)  { 
    return  str;

The Handlebars.registerHelper method takes the name of the helper and the helper function as arguments. Handlebars.js then takes whatever is returned from the helper function and writes it out to the template, so be sure to always return a string from your custom helpers.

Params object

Adding a third argument, params, to the call to helper.register will pass in grunt and assemble so that they may be used from inside helpers:

module.exports.register = function (Handlebars, options, params)  { 
  Handlebars.register('awesome', function ()  { 

Loading Helpers

Minimatch patterns can be used in the helpers option, and they'll look inside your devDependencies for any node modules that it finds. If it finds modules, it will attempt to load those as helpers.

Requirements for use:

  • Install the module and save to devDependcies
    • npm install my-custom-helper-module --save-dev
  • Add a pattern or the entire name to use that module in the options
    • options: { helpers: ['*-helper-module'] } }
  • Enjoy

Developing Custom Helpers

Passing assemble.options into helpers

Any value from assemble.options may be passed to helpers when the helper defines the register method. For example:

Given our Gruntfile.js has the following assemble task configuration:

assemble: {
  options: {
    version: '0.1.0', // or we could use '<%= pkg.version %>' 

And given we have defined a custom helper, opt, which gets properties from the assemble.options object and returns them:

module.exports.register = function (Handlebars, options)  { 
  Handlebars.registerHelper('opt', function (key)  { 
    return  options[key] || '';

We can now user our helper in a Handlebars template like this:

<div>Version: v{{opt 'version'}}</div>

And the output would be something like:

<div>Version: v0.1.0</div>

Quickstart using grunt-init

1. Install grunt-init

If you haven't already done so, install [Grunt][grunt] and grunt-init:

npm i -g grunt-cli grunt-init

Windows users, see the documentation for the correct destination directory path.

Once grunt-init is installed, place the template in your ~/.grunt-init/ directory. It's recommended that you use git clone to install this template into that directory as follows:

2. Install grunt-init-helper

git clone ~/.grunt-init/helper

3. Install dependencies

Then, in the directory where your custom helpers will be stored, run grunt-init helper and follow the prompts to generate a new helper with placeholder code that should be customized.

Note that you may also force grunt-init to use custom default values, move the defaults.json file to your ~/.grunt-init/ directory, and customize the values in that file.

Conventions and Recommendations

If you are creating a helper for distribution, then you might consider using grunt-init-assemble first to create a new Assemble project, then use grunt-init-helper to generate the new helper.

We recommend that you save the helper to the root of the project to make it easy for others to consume via package managers, such as Bower.

Naming Conventions

  • project name: It is recommended that you use the following pattern: "assemble-helper-[custom helper name]" (with helper being singular or plural).
  • helper name: Name the helper itself something like "helper-[helper-name].js". All "official" helpers have been created following the pattern "helper-*.js" so that they can easily be consumed by assemble.options.helpers via simple minimatch patterns. This doesn't prevent them from being used elsewhere either.

"Generalizing" code

Oftentimes, beyond being used as a Handlebars helper, the code for many helpers can easily be generalized so that they can also be used as Lo-Dash mixins, filters for other template engines etc. It's worth doing this whenever you can to make the helper more useful to others. Also:

  • Make sure you add a main property to the project's package.json with a path to the helper.
  • Register the helper with Bower and add a bower.json for easy downloading and consumption of the helper.
  • Add a test folder with any tests
  • If you want to demonstrate the helper, add those to the test folder as well

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