Ruby-on-Rails ERB vs HAML

#ruby #rails

original content is here : https://alsohelp.com/blog/erb-vs-haml

This is an opinionated article about ERB and HAML with Rails. Let's compare each other and pick a winner.

Use case

In the Ruby-on-Rails world, they are known as templating languages. In the MVC concept, they represent "the View". Both are here to output HTML.

Example

Examples worth a thousand words, so here are two examples, one with ERB, the other with HAML. Both are strictly equivalent. I tried to put different kinds of concepts in order to highlight various problems : create variables, run ruby code, inline style, condition, loop, etc.

ERB template file

<% v = run_some_ruby_code %>

<div id="main" style="margin-left: 0">

  <div class="left column">
    <h2>Welcome to the library</h2>

  <% books.each_with_index do |book, indx| %>
      <% if indx > 0 %>
      <p><%= book.title %></p>
    <% end %>
  <% end %>
  </div>


  <div class="right column">
    <%= render "shared/sidebar" %>
  </div>

</div>

Is equivalent to this HAML template file :

- v = run_some_ruby_code
#main{style: "margin-left: 0"}
  .left.column
    %h2 Welcome to the library
    - books.each_with_index do |book, indx|
      - if indx > 0
        %p= book.title
  .right.column
    = render "shared/sidebar"

ERB

Plain HTML is still valid, so copy/pasting from other websites is not a problem
Indent as you like : maybe seen as an advantage : if you'd like to indent it the way you want. Could also be seen as a problem : bad indentation still works...
Standard with the Rails default stack : that mean more standardisation : better IDE support, legacy app may use it more, and a lowest barrier entry

HAML

HAML is a lot less verbose - this is the main unfair advantage of HAML.
HAML must be correctly indented. Sometimes the indentation is not as intuitive as it should. So it's not so cool.
HAML is also not very intuitive for corner cases (javascript tags, inline CSS...). In this case, you have to use an external online tool.
Added as a gem, i.e. not included in a default Rails application
Known as slower than ERB - I didn't notice any practical difference though.

And the winner is

ERB.

I've used both and I have to say HAML has one very big advantage : a lot less verbosity. This is very handy for large template files. But large template files are not so frequent in an application if you properly cut them into small pieces - partial or view_components.

So now HAML's big one advantage doesn't outweigh the sum of its disadvantages : hard to copy/paste from examples, and tricky corner cases notably.

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