Extending Alterant

Adding new helpers

Alterant helpers can be written in both Ruby and Javascript. Ruby helpers have a limitation that means they can only return a simple Javascript hash (see examples of YamlReader and JsonReader). Javascript helpers share the same limitations as with the rest of the modifiers: no IO and file access.

Add a new Ruby helper

Here is the code for JsonReader helper, written in Ruby (as it requires file access):

module Alterant
	module Classes
		class JsonReader
			attr_reader :value

			def call(file)
				if @alter.basedir.nil?
					raise ::Alterant::RuntimeError, 'no basedir set'

				content = File.read(File.join(@alter.basedir, file))
				return ::JSON.load(content)

			def initialize(alter, context)
				@context = context
				@alter = alter


The file should be located under the classes folder of the gem. When JsonReader is called from within the modifier, the call method is called with the passed in parameters from Javascript and result is returned to the modifier as a hash.

Add a new Javascript helper

Here is the Containers helper, written in Javascript:

class Containers {
    constructor(containers) {
        this.containers = containers

    by_name(name) {
        for (var c in this.containers) {
            var item = this.containers[c]
            if (item.name == name) {
                return item

        return null