What is therubyracer or libv8 for in a rails application?

Asked 14/1, 2015 at 0:54 Answered 30/6, 2016 at 18:57

I was working on a project and was having issues with therubyracer and libv8 often, so i decided to remove them. It seemed to be the only thing that used them as a dependency was less-rails which I wanted to remove anyways.

My main question is what are they for and do I need them in the average application and if so why?

Cycloplegia answered 14/1, 2015 at 0:54 Comment(3)

They are generally used for the asset pipeline on platforms that don't have a JavaScript runtime installed by default. So if you do not compile assets on the target system or the system has a JavaScript runtime in the path they are not needed. – Roomful 14/1, 2015 at 0:59

So a CentOS server that is not connected to the internet would or would not have this? – Cycloplegia 14/1, 2015 at 1:16

If the server already has a JavaScript runtime such as node.js already installed it isn't needed. I don't know if centos comes with a JavaScript runtime also if you are not compiling assets on te box it isn't needed. Less.rb has a dependency on commonjs which appears to only use therubyracer or therubyrhino Check out the answer here for more info. #18688075 – Roomful 14/1, 2015 at 4:29

There are a few things for which a Rails app might use a Javascript Runtime:

1) The Rails Asset Pipeline requires a Javascript Runtime in order to perform Javascript compression.

2) Certain Rails ActionView Helpers like javascript_include_tag require a Javascript Runtime in order to execute Javascript functions.

Not every Rails application use those features, hence the reason that therubyracer gem is initially commented out in your Gemfile; Furthermore note that you could alternatively use NodeJS as your Javascript runtime.

For details, see:

http://guides.rubyonrails.org/asset_pipeline.html#javascript-compression

http://www.rubydoc.info/docs/rails/ActionView/Helpers/JavaScriptHelper

http://www.rubydoc.info/docs/rails/ActionView%2FHelpers%2FAssetTagHelper%3Ajavascript_include_tag

Proper "Rails" way to perform javascript on specific pages

Fathomless answered 30/6, 2016 at 18:57 Comment(0)

rubyracer provides following features:

 1. We can write your ruby codes inside js codes. 
 2. We can invoke the js functions from ruby codes.  
 3. Manipulation of javscript objects & the passing them to javascript functions.

Those are the few basic benefits of using rubyracer gem. Please read complete details here

Magnanimous answered 14/1, 2015 at 1:2 Comment(5)

item 1, does that have anything to do with js.erb files? – Cycloplegia 14/1, 2015 at 1:5

when you are hitting your rails controller (via ajax) and want some interaction you need to your codes in your app/views/action_name.js.erb file. This file will hold your js codes + embedded ruby codes as well. :) Please check : richonrails.com/articles/basic-ajax-in-ruby-on-rails – Magnanimous 14/1, 2015 at 1:10

In the provided link just search for app/views/products/_save.js.erb: That will clear your doubt :) – Magnanimous 14/1, 2015 at 1:11

sounds terrible, why would we want to invoke ruby code form js or vice versa ? – Homemade 15/3, 2016 at 4:49

OOPS!! I take my words back... I had to run JS inside Java (to port a template system to java github.com/nishants/jeyson, github.com/nishants/wirestub) ..If I ever need Sinatra/Rails port, will have to try the rubyracer...... too bad there is no pure ruby alternative like Nashorn for Java . – Homemade 20/10, 2016 at 19:20

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