Block comments in html.erb templates in rails

Question

How do you comment out html mixed with ruby code?

some text <% ... %> more text <%= ... %>
something else
<% ... %>

---

In jsp it's real simple: <%-- ... --%>, but I'm unable to find any concise option in rails.

Simple html comments <!-- ... --> do not work: ruby code is still executed and yells errors.

There's an option to use if false with html comments, but it's quite verbose, not to mention IDEs doesn't support it.

---

There's also an option coming from pure ruby, which surprisingly works.

<%
=begin %>
... html and ruby code goes here
<%
=end %>

It's generally fine, except that it's verbose, weird-looking and none of ruby IDEs I know support it (yep, I like to comment/comment-out with one keystroke).

---

I'm curious, is there any 'official' of doing this in rails?

Answer 1

I wouldn't count as a solution, but perhaps enclosing the chunk between an

<% if false %>
   ...
<% end %>

or if you feel a little dirty, create a helper that simply outputs nothing.

I've never needed it, but I'm stumbled there seems to be no out-of-the-box solution for this.

Answer 2

After =begin you do not need to put %>

<%
=begin

code code code code code code 
code code code code code code 
code code code code code code 
code code code code code code 

=end %>

Answer 3

<% %w(
  <span title="<%= title %>">hello</span>
) %>

I hope I've just blown your minds!

Answer 4

<%#=

...commented
multiline
block...

%>

Answer 5

You can use both <%if false%> and HTML comments at the same time:

<%if false%><--

stuff to comment out

--><%end%>

The benefits are:

• Ruby code is not executed

• The commented block has gray color in IDE

• The intention is obvious for other developers

Answer 6

Just an addendum to some of the previous answers. I found the =begin/=end solution most useful, but for the sake of beauty I write it like so:

<%
=begin
  <p>HTML will be ignored</p>
  <%= 'and so will ruby' %>
  <p>
    <%= 'plus the whole block will be greyed in editor' %>
  </p>
=end
%>

Note that since everything is ignored until the =end there is no need to close the =begin tag with %> or open the =end tag with <% (which has also been pointed out in an earlier answer)

I found this to be the most elegant solution to completely outcomment a block of mixed ruby and html code and have it greyed out in my editor as well, as opposed to the <% if false %> solution. Only drawback is that =begin and =end must be placed at the very beginning of the line..

Answer 7

This is the onlyone that worked for me.

<%
=begin %>

code code code code code code 
code code code code code code 
code code code code code code 
code code code code code code 

<%
=end %>

Answer 8

Since you can use <% %> to put a ruby block, it can be certainly used to put in comments into it.

A simpler and elegant solution would look like...

<%
# See! I am a Ruby Comment
# And I am multi-line
# I look like a recognizable ruby comment block too
# and not so complex
# The only drawback with me is the Hash symbol you have to repeat
# But it's the norm, isn't it?
%>

Answer 9

The =begin approach is annoying because:

1. It doesn't work for mixed HTML and Ruby (or just HTML) that's on a single line
2. It's annoying to type

The <% if false %> approach works, but it looks weird and doesn't give anyone else who looks at your code a hint about your intentions.

My solution is as follows:

In application_helper.rb, add a method so:

def comment
end

Then in your view template, you can say:

<% comment do %>Some stuff that won't be rendered...<% end %>

This works because any Ruby method can take a block, but will silently ignore the passed-in block if your method doesn't include a yield.

Answer 10

Use this for commenting single lines:

<%# your_ruby_code %>

For multiple lines, the following you said would work:

<% =begin %>  
<% ruby_code %>
<% =end %>

Answer 11

You have to bear in mind where the code is executed. Ruby-style comments work because the Ruby code is executed on the server before it is served to the web browser. This also explains why HTML comments do not work—the Ruby has already been executed.

Doesn't the IDE you're using support creating custom macros for commenting out blocks of code?

Answer 12

Use a HEREDOC called comment

Pros:

• Self-explanatory that this is a comment
• Works for erb and HTML tags
• Has ok syntax highlighting (as one long string)

Cons:

• Weird 3 line closing syntax
• No keyboard shortcuts

Code:

The opening tag can be

<% <<-COMMENT %>

the above closing erb tag is just for looks (to match the end),
but don't put anything else there, it may show up on the page

or

<%
<<-COMMENT
%>

Anything here won't run or show up in the browser

<P>
    this will NOT be displayed in the browser
    <strong> not even in the developer's tools </strong>
</p>

<% 1_000_000_000_000.times do |count| %>

for the <%= count %>'th time, this won't run a trillion times,
this is all just a string

all of these %>, <%, <% end %>, end, do, <!--, won't cause any issues.

but the below opening erb tag is important (if you used any erb tags in the comment).
I have no clue why?

The closing tag

yes it needs to be 3 lines . I don't know why the opening erb tag is important but it is! (unless you didn't use any erb tags in the comment).

<%      
COMMENT
%>

Answer 13

Sublime Text's block comment shortcut ctrl+shift+/ notices whether you've selected normal HTML or an Erb tag and puts either the <!--- or <% =begin %> accordingly.

Answer 14

To comment out erb tags use the ruby comment hash symbol before the = sign in the opening tag: <%=. To comment out in HTML, use <!-- -->.

<p>
 1. This is some text I want to keep
 <%= @some_object.some_attribute %>
</p>

<p>
  2. I want to keep this text but comment out the erb tag
  <%#= @some_object.another_attribute %>
</p>

<!--
<p>
  3. I want all of this text commented out including the erb tag
  <%#= @some_object.some_attribute %>
</p>
-->

<!--
<p>
 4. I just want this html commented out but I want to keep the erb tag
 <%= @some_object.some_attribute %>
</p>
-->

Answer 15

One way

This is my preferred way.

<%# START COMMENTED OUT SECTION %>
<%if false%><-- 

your view code here....

--><%end%>
<%# END COMMENTED OUT SECTION %>

You might say, why on earth would you want massive caps locks sentences in your code? The answer is because it's easy to forget (or simply not know) what <%if false%><-- is doing, or what --><%end%> is doing. A sleepy or uncaffeinated developer could easily delete them thinking they were typos, which would not be good! That's why I try to be kind to myself/other developers and make it super obvious. It's not succinct or pretty, but it's very practical and almost foolproof.

Second way

This method is great for being:

• Simple
• Not idiosyncratic (i.e. uses normally formatted ruby)
• Expressive: conveys the meaning of what's happening (someone can easily figure out what it's doing)
• Minimal

And here it is:

<%#

multiple
lines
commented 
out

%>

Answer 16

The only acceptable solution I ever found to this back-breaking problem was to put a space within the "<%=" to make it no longer register as ruby code, and then comment out the whole block with html comments

Like this:

<!--
<p>
  < %= @some_object.some_attribute %>
</p>
<p>
  < %= @some_object.another_attribute %>
</p>
<p>
  < %= @some_object.some_attribute %>
</p>
<p>
  < %= @some_object.some_attribute %>
</p>
-->

Yes, adding the spaces is annoying. But it is the least annoying of all the solutions I've yet seen.

Answer 17

For block comments in templates, my text editor (Komodo) finds this variation on @Garfield's recommendation least obnoxious:

<%# A long multiline comment in a rails template ...
  # line 2
  # and so on ... 
  # %>