While building a textarea component for RapidRails UI, I discovered an interesting Rails behaviour that affects any textarea rendering, whether in regular views or ViewComponents:

Version 1: Adds unwanted whitespace

<%= tag.textarea(...) do %>  
  <%= value %>
<% end %>

Result when value is " Hello ":

<textarea>
    Hello
</textarea>

Version 2: Preserves exact content

<%= tag.textarea(...) do %><%= value %><% end %>

Result when value is "Hello":

<textarea>Hello</textarea>

Why?!

The behaviour stems from Rails' ActionView template handling system. Specifically, in the content_tag helper:

1. The `content_tag` helper in ActionView:

# actionview/lib/action_view/helpers/tag_helper.rb

def content_tag(name, content_or_options_with_block = nil, options = nil, &block)
  if block_given?    
    content = capture(&block)  # Captures ALL whitespace  
  end
end

The capture method preserves all whitespace within the block, including:

Newlines after the opening do
Indentation before the content
Newlines before the end

2. Rails' own form helper avoids this by not using blocks:

# actionview/lib/action_view/helpers/tags/text_area.rb
def render  
  content_tag("textarea", value_before_type_cast, options)
end

By passing the content directly rather than using a block, it sidesteps the whitespace preservation.

Why It matters

The whitespace preservation is critical for:

Character count accuracy
Form validation
Content formatting
User experience
Data consistency

Best Practices

1. Use inline ERB for textarea content:

<%= tag.textarea(...) do %><%= value %><% end %>

2. Or use Rails' direct approach:

<%= content_tag("textarea", value, options) %>

While both solution behave the same, choose what you like.

RapidRails is using content_tag approach:

Matches Rails' native implementation
No whitespace concerns at all
More straightforward
Less prone to formatting issues
Cleaner code

3. Document this behaviour in your components/views for future reference.

This behaviour isn't a bug—it's how Rails templates preserve whitespace. However, textareas are special because they preserve whitespace in HTML, making them more sensitive to these template formatting issues.

📚 More reads

Ahmed Nadar

Rapid Rails

Common Issues with Rails Textarea Whitespace Behaviour

Why?!

Why It matters

Best Practices