Quick Ruby implementation of https://www.npmjs.com/package/clsx

clsx.rb

module Clsx
  def clsx(*args)
    process_args = args.map do |arg|
      if arg.is_a?(Array)
        clsx(*arg)
      elsif arg.is_a?(Hash)
        arg.map do |key, value|
          key if value
        end
      else
        arg
      end
    end

    process_args
      .flatten
      .compact
      .keep_if { |arg| arg && arg.to_s.strip != "" }
      .join(" ")
  end
end

test.rb

require "minitest/autorun"
require "./clsx"

class TestClsx < Minitest::Test
  include Clsx
  def test_a_simple_list
    assert_equal "foo bar baz", clsx("foo", "bar", "baz")
  end

  def test_a_hash_of_items
    assert_equal "foo baz", clsx("foo" => true, "bar" => false, "baz" => true)
    assert_equal "foo baz", clsx(foo: true, bar: false, baz: true)
  end

  def test_an_array
    assert_equal "foo bar baz", clsx(["foo", "bar", "baz"])
  end

  def test_an_array_with_falsey_things
    assert_equal "foo bar baz", clsx(["foo", nil, false, "bar", "", "baz"])
  end

  def test_a_variadic_array_of_trash
    # The javascript version evaluates 0 as falsey
    assert_equal "foo bar baz hello there", clsx(["foo"], ["", false, "bar"], [["baz", [["hello"], "there"]]])
  end

  def test_the_kitchen_sync
    assert_equal "foo bar hello world cya", clsx("foo", [1 && "bar", {baz: false, bat: nil}, ["hello", ["world"]]], "cya")
  end
end