Rails Interview Questions

I get a fair number of questions via Hacker Hours and elsewhere regarding what questions to use/expect in an interview for a Rails developer, so figured I would get it together in a tidy list. Pull requests welcome.

Tips

Interviewers

• Personalize your list of questions.
• Don't ask questions you don't know the answers to.
• Mix trivia questions with open-ended ones.
• Use Codr or a similar online collaborative text editor for doing coding challenges
  • Can be seen in real-time by remote team members
  • The unique URL with the solution can be easily sent around or added wherever you a tracking information about the candidate
• About a third of the way through the interview, however you're feeling about the candidate (👍/👎), try and convince yourself otherwise.
  • This is to help yourself fight your own biases.

Interviewees

• Don't study to the test. Not all of these questions will be used, and others will be asked that aren't covered here. Know your stuff.
• Rails skills != CS skills
• Know whether you are interviewing for a full-stack vs. backend-focused position.
• Have code up on Github/Bitbucket/wherever - the more side projects you have to talk about, the better.
• Be comfortable with some version control system.
• Community awareness and resourcefulness can be as important as technical knowledge.

The Questions

General

• What is a tree? What is a DAG?
• Pseudo-code depth-first and breadth-first search.
• Given a sorted array, what is the fastest way to find a element? What is the Big-O time to do so?
• Explain how ajax works, hitting all parts of the stack. (@abestanway)

Ruby

• What is the difference between a lambda, a block and a proc? [I have gotten this one at every Ruby interview I've been in]
• How do you sort an Array of objects by a particular attribute? What is a better way to do sorting with ActiveRecord?
• What are some of your favorite gems? What are their alternatives?
• In Ruby, which is generally the better option: a recursive function or an iterative one?
• What are #method_missing and #send? Why are they useful?
• What are the various Ruby runtimes, and how are they different?

Rails

• What is the general history of Rails?
• What is new in Rails 4?
• Explain the different pieces of Rails.
• Walk through the flow of a request through Rails.
• What are the different server options for running a Rails/Rack app?
• Explain CSRF and how Rails combats it.
• Explain mass-assignment vulnerability.
• Why do some people say "Rails can't scale"?
• What is Rack?
• What is middleware? How does it compare to controller filters/actions?
• Explain various forms of caching available in Rails.
• What are some Ruby web server options?
• How is something like 30.seconds.ago implemented? (c/o @harrisj)
• On a scale of "I've heard of it" (0) to "I maintain it" (10), how would you rate your Rails proficiency?

Resources

(no particular order)

• @darcyclarke's Frontend Interview Questions (inspiration for this repo)
• My Advanced JavaScript class materials
• Video of the Junior Developer Panel that I hosted
• Ruby Koans
• Project Euler
• Flatiron School Prework and background
• Job Interview by @ruby-jokes
• Developer Evangelist Interview Questions
• Resources from Hacker Hours
• Technical interview cheat sheet

Rails Interview Questions by Aidan Feldman is licensed under a Creative Commons Attribution 3.0 Unported License.