title: Problem deploying Rails 3.1 project to Heroku: Could not find a JavaScript runtime
body: <p>I am having trouble deploying a rails 3.1 beta project to heroku. The problem happened at the database migration step. When I ran:</p>
  
  <pre><code>heroku rake db:migrate
  </code></pre>
  
  <p>I got error message:</p>
  
  <pre>
  > rake aborted! 
  
  > Could not find a JavaScript runtime. See
  > https://github.com/sstephenson/execjs
  > for a list of available runtimes.
  
  > /app/Rakefile:5 
  
  > (See full trace by running task with --trace) 
  
  > (in /app)
  </pre>
  
  <p>But I can successfully run the application locally, and I do have nodejs installed. Any idea why?</p>
  
  <p>Here my gem list:</p>
  
  <pre><code>abstract (1.0.0)
  actionmailer (3.1.0.beta1)
  actionpack (3.1.0.beta1, 3.0.7)
  activemodel (3.1.0.beta1, 3.0.7)
  activerecord (3.1.0.beta1)
  activeresource (3.1.0.beta1)
  activesupport (3.1.0.beta1, 3.0.7)
  ansi (1.2.5)
  arel (2.1.0)
  bcrypt-ruby (2.1.4)
  builder (3.0.0, 2.1.2)
  bundler (1.0.13)
  coffee-script (2.2.0)
  coffee-script-source (1.1.0)
  configuration (1.2.0)
  daemon_controller (0.2.6)
  erubis (2.7.0, 2.6.6)
  execjs (1.0.0, 0.3.3)
  fastthread (1.0.7)
  heroku (2.1.4)
  hike (1.0.0)
  i18n (0.6.0beta1, 0.5.0)
  jquery-rails (1.0.1)
  json (1.5.1)
  json_pure (1.5.1)
  launchy (0.4.0)
  mail (2.3.0)
  mime-types (1.16)
  minitest (1.6.0)
  multi_json (1.0.1)
  mysql (2.8.1)
  mysql2 (0.3.2)
  oauth (0.4.4)
  passenger (3.0.7)
  polyglot (0.3.1)
  rack (1.3.0.beta, 1.2.2)
  rack-cache (1.0.1)
  rack-mount (0.7.2, 0.6.14)
  rack-ssl (1.3.2)
  rack-test (0.6.0, 0.5.7)
  rails (3.1.0.beta1)
  railties (3.1.0.beta1)
  rake (0.8.7)
  rdoc (2.5.8)
  rest-client (1.6.1)
  rubygems-update (1.8.1)
  sass (3.1.1)
  simplegeo (0.5.1)
  sprockets (2.0.0.beta.2)
  sqlite3 (1.3.3)
  sqlite3-ruby (1.3.3)
  term-ansicolor (1.0.5)
  therubyracer-heroku (0.8.1.pre3)
  thor (0.14.6)
  tilt (1.3)
  treetop (1.4.9)
  turn (0.8.2)
  tzinfo (0.3.27)
  uglifier (0.5.1)
  </code></pre>