Does Rails rake db:migrate needs a javascript runtime? - Stack Overflow

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In my first rails project (using mysql) I tried to execute the rake db:create mand, but it outputted the following error:

Could not find a JavaScript runtime. See for a list of available runtimes.

So I included gem 'therubyracer', require: "v8" on my Gemfile and executed a bundle install. The problem is solved, but it left some doubts.

Could somebody give me an explanation about why a javascript runtime is needed for this kind of task? I'm new to Ruby and RoR so this seems quite strange to me, why do RoR use javascript for creating a database?

In my first rails project (using mysql) I tried to execute the rake db:create mand, but it outputted the following error:

Could not find a JavaScript runtime. See https://github./sstephenson/execjs for a list of available runtimes.

So I included gem 'therubyracer', require: "v8" on my Gemfile and executed a bundle install. The problem is solved, but it left some doubts.

Could somebody give me an explanation about why a javascript runtime is needed for this kind of task? I'm new to Ruby and RoR so this seems quite strange to me, why do RoR use javascript for creating a database?

• ruby-on-rails
• rake
• javascript

Share Improve this question Follow edited Dec 1, 2011 at 14:36 marcio asked Dec 1, 2011 at 14:20 marciomarcio 10.5k1313 gold badges5757 silver badges8686 bronze badges 5

• 1 What library did raise that error? Try again without the rubyracer and with rake db:create --trace – Reactormonk Commented Dec 1, 2011 at 14:23
• 1 probably coffee-rails and uglifier – Ben Commented Dec 1, 2011 at 14:24
• That's it @Ben, coffee-rails was causing the dependency! – marcio Commented Dec 1, 2011 at 15:07
• Thanks @tass, didn't know about the --trace parameter – marcio Commented Dec 1, 2011 at 15:07
• +1 for asking this question as i faced same problem. – Neeraj Commented Jan 28, 2013 at 8:12

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2 Answers 2

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You need a javascript runtime because now Rails uses an asset pipeline. Rails doesn't need it to run your migrations but when you run rake db:migrate, the rake task loads your rails application that needs a javascript runtime to start. Practically, there is no relation between the migrations and the javascript runtime but your app won't load without it.

This is for serverside executed javascript. It is used by NodeJS, Coffeescript and quite a few more javascript gems. If you dont use any of those, you can just remove them from your gemfile and no runtime will be required.

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