clsx-rails

A tiny Rails view helper for constructing CSS class strings conditionally.

This gem is essentially a clone if the clsx npm package. It provides a simple way to conditionally apply classes to HTML elements in Rails views. It is especially useful when you have a lot of conditional classes and you want to keep your views clean and readable.

Ruby 3.1+ and Rails 7.0+ are supported.

Install the gem and add to the application's Gemfile by executing:

bundle add clsx-rails

Or add it manually to the Gemfile:

gem 'clsx-rails', '~> 1.0'

The clsx helper method can be used in views to conditionally apply classes to HTML elements. You can also use a slightly more conise cn alias. It accepts a variety of arguments and returns a string of unique classes.

# Strings (variadic)
clsx('foo', true && 'bar', 'baz')
# => 'foo bar baz'

# Hashes
cn({ foo: true, bar: false, baz: a_method_that_returns_true })
# => 'foo baz'

# Hashes (variadic)
clsx({ foo: true }, { bar: false }, nil, { '--foobar': 'hello' })
# => 'foo --foobar'

# Arrays
cn(['foo', nil, false, 'bar'])
# => 'foo bar'

# Arrays (variadic)
clsx(['foo'], ['', nil, false, 'bar'], [['baz', [['hello'], 'there']]])
# => 'foo bar baz hello there'

# Kitchen sink (with nesting)
cn('foo', ['bar', { baz: false, bat: nil }, ['hello', ['world']]], 'cya');
# => 'foo bar hello world cya'

<%= tag.div class: clsx('foo', 'baz', 'is-active' => @active) do %>
  Hello, world!
<% end %>

<div class="<%= clsx('foo', 'baz', 'is-active' => @active) %>">
  Hello, world!
</div>

%div{class: clsx('foo', 'baz', 'is-active' => @active)}
  Hello, world!

div class=clsx('foo', 'baz', 'is-active' => @active)
  | Hello, world!

So the basic idea is to get rid of constructions like this in your views:

<% classes = ['foo', 'baz'] %>
<% classes << 'is-active' if @active %>

<div class="<%= classes.join(' ') %>">
  Hello, world!
</div>

or like this:

<div class="<%= ['foo', 'baz', @active ? 'is-active' : nil].compact.join(' ') %>">
  Hello, world!
</div>

or like this:

<div class="foo bar <%= 'is-active' if @active %>">
  Hello, world!
</div>

This gem reproduces the functionality of the original clsx package, but with nuances of Ruby and Rails in mind.

The main differences are:

1. falsy values in Ruby are only false and nil, so the clsx method will not accept 0, '', [], {}, etc. as falsy values.

    clsx('foo' => 0, bar: []) # => 'foo bar'

2. clsx-rails supports complex hash keys, like { %[foo bar] => true }, which will be converted to foo bar in the resulting string. Meaning, if it's a valid input for the clsx-rails, it's a valid hash key.

    clsx([{ foo: true }, 'bar'] => true) # => 'foo bar'

3. clsx-rails will ignore objects that are blank?, boolean (true or false), or an instance of Proc (so, procs and lambdas).

    clsx('', [], {}, proc {}, -> {}, nil, false, true) # => nil

4. clsx-rails returns nil if there are no classes to apply, instead of an empty string. The reason for that is not to pollute the HTML with empty class attributes when using Rails tag helpers: Rails will not render the class attribute if it's nil.

     clsx(nil, false) # => nil

   Although, it won't help if you're using it directly in erb:

    <div class="<%= clsx(nil, false) %>">
      Hello, world!
    </div>

   This code will render <div class="">Hello, world!</div> anyway.

5. clsx-rails eliminates duplicate classes:

    clsx('foo', 'foo') # => 'foo'

After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and the created tag, and push the .gem file to rubygems.org.

There is a simple benchmark script in the benchmark directory. You can run it with bundle exec ruby benchmark/run.rb. I've added it for easier performance testing when making changes to the gem.

This project uses Conventional Commits for commit messages.

Types of commits are:

• feat: a new feature
• fix: a bug fix
• perf: code that improves performance
• chore: updating build tasks, configs, formatting etc; no code change
• docs: changes to documentation
• refactor: refactoring code

Bug reports and pull requests are welcome on GitHub at https://github.com/svyatov/clsx-rails.

The gem is available as open source under the terms of the MIT License.