A simple gem to merge HTML attributes in Ruby. It's incredibly useful when you're working with HTML attributes in a Rails app.

For example, you're accepting arguments in a component or partial from somewhere else that you then need to merge smartly (can be tailwind classes, data attributes for stimulus controllers, etc)

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

$ bundle add html_attrs

html_attrs = {
  class: 'bg-primary-500', data: { controller: 'popover', action: 'click->popover#toggle' }
}

html_attrs = html_attrs.smart_merge(
  class: 'border border-primary-500', data: { controller: 'slideover' }, href: '#'
)

# Will produce:
{
  class: 'bg-primary-500 border border-primary-500',
  data: { controller: 'popover slideover', action: 'click->popover#toggle' },
  href: '#'
}
# Note: #smart_merge returns an HtmlAttrs object which is a subclass of Hash, so you can use it just like a hash.

You can use this in helpers that accept HTML attributes as a hash, e.g:

<%= content_tag(:a, 'Hello', html_attrs) %>

<%# Will produce: %>
<a
  class="bg-primary-500 border border-primary-500"
  data-controller="popover slideover"
  data-action="click->popover#toggle"
  href="#"
>
  Hello
</a>

You can also use the to_s method to get the string representation of the HTML attributes, if you need to use it in a string context.

<a <%= html_attrs.to_s %> id='home'>Hello</a>

<%# Will produce: %>
<a
  class="bg-primary-500 border border-primary-500"
  data-controller="popover slideover"
  data-action="click->popover#toggle"
  href="#"
  id='home'
>
  Hello
</a>

Merging is done recursively:

• Strings are merged by concatenating them with a space.
• Arrays are merged with simple concatenation.
• Hashes are merged recursively using the above rules.
• Everything else is merged normally, just like with Hash#merge.

Super simple, but super powerful.

If one hash that has a string key and the other has a symbol key or vice-versa, we'll convert everything to whatever the first hash has.

By default, this gem merges class, style and data attributes recursively. Which should usually be more than enough. You can easily customize this by specifying mergeable_attributes: when calling smart_merge. e.g:

HtmlAttrs.new(class: 'bg-primary-500', id: 'test', aria_label: 'Help')
  .smart_merge(aria_label: 'Another', href: '/test', mergeable_attributes: [:aria_label])
# => { class: 'bg-primary-500', id: 'test', aria_label: 'Help Another', href: '/test' }

You can also just set mergeable_attributes: :all to merge everything. Or you can just use smart_merge_all which merges everything by default.

{ class: 'bg-primary-500', id: 'test', aria_label: 'Help' }
  .smart_merge_all(class: 'text-red-500', aria_label: 'Another', href: '/test')
# => { class: 'bg-primary-500 text-red-500', id: 'test', aria_label: 'Help Another', href: '/test' }

Alternative, you can use the HtmlAttrs class directly, e.g:

HtmlAttrs.smart_merge(
  { class: 'bg-primary-500', data: { controller: 'popover' } },
  { id: 'test', class: 'border' }
)
# => { class: 'bg-primary-500 border', data: { controller: 'popover' }, id: 'test' }

Or, you can also instantiate a new HtmlAttrs object and use the smart_merge method, e.g:

html_attrs = HtmlAttrs.new(class: 'bg-primary-500', data: { controller: 'popover' })
# => { class: 'bg-primary-500', id: 'test', aria_label: 'Help', download: 'test.jpeg' }

html_attrs.smart_merge( id: 'test', class: 'border')
# => { class: 'bg-primary-500 border', data: { controller: 'popover' }, id: 'test' }

Under the hood, HtmlAttrs is a simple wrapper around Hash, so you can use it just like any other hash. The only difference is #smart_merge, #smart_merge_all and to_s.

I am working on a super-powerful Rails UI library - components as well as templates & patterns.

Please check this out if you're interested.

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.

Bug reports and pull requests are welcome on GitHub at https://github.com/owaiswiz/html_attrs.

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