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?

score 176 · Answer 1 · edited Mar 20 '23 at 08:39

176

Use this for commenting single lines:

<%# your_ruby_code %>

For multiple lines, the following you said would work:

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

edited Mar 20 '23 at 08:39

Cadoiz

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answered Jun 27 '10 at 16:53

Garfield

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it works if = is at start of new line just like in the answer – dhaval Jun 20 '14 at 06:39
what if it is like this <%= %> ? Where would the hash go - before or after the equals sign? – BenKoshy Oct 12 '15 at 22:37
I tried exactly that but with `<%` and `=begin %>` on the same line, which is ***much*** more intuitive. Why doesn't that approach work? – stevec Dec 19 '20 at 05:11
Did anyone check if you need a new line before `=begin` and `=end` [as dhaval said](https://stackoverflow.com/questions/3127644/block-comments-in-html-erb-templates-in-rails/3128066#comment37592942_3128066) or if [@stevec is right](https://stackoverflow.com/questions/3127644/block-comments-in-html-erb-templates-in-rails/3128066#comment115564360_3128066) and it just works like answered? – Cadoiz Mar 20 '23 at 08:40

score 133 · Accepted Answer · edited Jul 23 '11 at 16:14

133

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.

edited Jul 23 '11 at 16:14

Simon Perepelitsa

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answered Jun 27 '10 at 18:12

Chubas

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@Chloe Not quite sure why you directed your comment to me but you are quite correct `<%= false %>` would not work. You should try the solution provided though which would work `<% if false %>` without the = sign – jamesc Feb 14 '20 at 10:56
@jamesc Your comment was deleted before you saw my response. Someone deleted your comment where you said to use `<%# if false %>`. – Chloe Feb 20 '20 at 08:20

score 40 · Answer 3 · answered Jun 10 '14 at 00:29

40

The =begin approach is annoying because:

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

answered Jun 10 '14 at 00:29

sumizome

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You can even write it as <% comment do %>...<% comment end %>. I've added this syntax to sublime text so that It even looks like a real comment. – Mariano Cavallo Aug 31 '14 at 02:36
1

Lovely solution!! One improvement: commenting code to disable it is kind of a hack, so rather call the method `ignore` or `disable` and we get a fully semantic solution: `<% ignore do %>…<% end %>` – tanius Oct 12 '19 at 18:58

score 17 · Answer 4 · answered Jun 09 '14 at 10:07

17

<%#=

...commented
multiline
block...

%>

answered Jun 09 '14 at 10:07

Piotr Turek

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This answer should have way more interest. – Ulysse BN May 13 '19 at 08:39
1

As of Rails 6 at least, the `=` doesn't seem to be necessary. – David Moles Oct 02 '20 at 19:27
@david the `<%=` is just convention to say it previously was a `<%=`, not a `<%`. – Cadoiz Mar 20 '23 at 08:43
@lcjury did you read that he wrote `<%=`, not `<=`? – Cadoiz Mar 20 '23 at 08:44

score 11 · Answer 5 · edited May 23 '17 at 11:47

11

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 ... 
  # %>

edited May 23 '17 at 11:47

Community

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answered Mar 21 '13 at 15:40

klenwell

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As of Rails 6 at least, only the first `#` seems to be necessary. – David Moles Oct 02 '20 at 19:27
@David You're right, but the point of the answer seems to be that the code editor knows it's comments. – Cadoiz Mar 20 '23 at 08:45

score 6 · Answer 6 · edited Mar 20 '23 at 08:54

6

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>
-->

edited Mar 20 '23 at 08:54

Cadoiz

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answered Jul 23 '11 at 16:28

jamesc

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As far as I understand, he's looking for a multiline comment-out solution: If I have a block of n lines, I just want to be able to add a line at the top and the bottom (or maybe a couple) and have it work. I don't want to have to edit the whole block. – dionyziz Oct 23 '13 at 21:48

score 5 · Answer 7 · answered Aug 30 '14 at 12:20

5

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?
%>

answered Aug 30 '14 at 12:20

Sagar Ranglani

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This doesn't work. Any ruby tags inside the block comment will close the outer block. – Hovis Biddle Aug 04 '16 at 19:20

score 5 · Answer 8 · answered Feb 15 '16 at 13:39

5

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 %>

answered Feb 15 '16 at 13:39

Michal

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This one works well for both HTML and Ruby code. Thanks! – DariusP Jun 09 '22 at 09:10

score 5 · Answer 9 · answered May 22 '18 at 13:00

5

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..

answered May 22 '18 at 13:00

ViggoV

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I am getting this error: "embedded document meets end of file" – Kieran Andrews Feb 14 '19 at 01:26
I get that error too. Any solution? – Basil Aug 22 '22 at 17:43
Isn't this a duplicate of [this answer](https://stackoverflow.com/a/35410866/4575793)? – Cadoiz Mar 20 '23 at 08:50

score 4 · Answer 10 · edited Mar 20 '23 at 08:48

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
%>

score 3 · Answer 11 · edited Mar 20 '23 at 08:51

3

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

edited Mar 20 '23 at 08:51

Cadoiz

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answered May 23 '18 at 23:08

stillwaiting

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The commented block doesn't show grey colour in Sublime Text. – stevec Mar 28 '21 at 02:24

score 2 · Answer 12 · answered Jun 27 '10 at 16:02

2

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?

answered Jun 27 '10 at 16:02

John Topley

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1) you're right, jsp comments have slightly different format, I updated the post. 2) I can't find anything like that in IDEA or Netbeans. Did you have anything any particular IDE in mind saying this? – Nikita Rybak Jun 27 '10 at 17:25
1

No I didn't. Personally, I don't use an IDE for Rails projects. – John Topley Jun 27 '10 at 17:45

score 1 · Answer 13 · answered Dec 11 '12 at 21:46

1

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.

answered Dec 11 '12 at 21:46

iono

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Yes, but this still won't comment out both the HTML *and* the ruby. – Adamantish Oct 27 '15 at 19:52
Hmm... sounds like good cause for a custom plugin. Maybe as a stopgap, you could press `ctrl+d` to multi-select the start of every Erb tag `<%` within the block and then hit `ctrl+shift+/`, then hit it once more for the whole block to comment out the HTML. – iono Oct 28 '15 at 04:16
Why is everybody talking about sublime here? It doesn't appear to me as part of the question. – Cadoiz Mar 20 '23 at 08:56

score 1 · Answer 14 · answered Jul 16 '20 at 20:58

1

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

I hope I've just blown your minds!

answered Jul 16 '20 at 20:58

DTrejo

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score 0 · Answer 15 · edited Mar 20 '23 at 08:57

0

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 %>

edited Mar 20 '23 at 08:57

Cadoiz

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answered Feb 08 '16 at 13:38

Platon

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stevec · Answer 16 · 2021-04-17T03:39:53.180

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

%>

But this wont work when there is ERB code in one of the lines..For Ex — Mithun Nair, Feb 03 '21 at 06:59

score -4 · Answer 17 · answered Nov 03 '16 at 20:15

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.

You might as well just add a `#`... instead of sending ruby in the document. — max, Apr 25 '17 at 02:57

Block comments in html.erb templates in rails

17 Answers17

Use a HEREDOC called comment

Pros:

Cons:

Code:

One way

Second way

Linked

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