Could not find a JavaScript runtime

Rails3.1下报出下面的错误：

 

/gems/execjs-1.1.2/lib/
execjs/runtimes.rb:43:in `autodetect’: Could not find a JavaScript
runtime.

 

Gemfile中添加：

 

gem 'execjs'

gem 'therubyracer'

 

执行：

 

bundle install

 

即可。