我创建了一个rails应用程序,并尝试启动rails服务器.我得到以下错误：
/home/ritesh/.rvm/gems/ruby-1.9.3-p429/gems/execjs-2.0.1/lib/execjs/runtimes.rb:51:in `autodetect': Could not find a JavaScript runtime. See https://github.com/sstephenson/execjs for a list of available runtimes. (ExecJS::RuntimeUnavailable) from /home/ritesh/.rvm/gems/ruby-1.9.3-p429/gems/execjs-2.0.1/lib/execjs.rb:5:in `<module:ExecJS>' from /home/ritesh/.rvm/gems/ruby-1.9.3-p429/gems/execjs-2.0.1/lib/execjs.rb:4:in `<top (required)>' from /home/ritesh/.rvm/gems/ruby-1.9.3-p429/gems/uglifier-2.2.1/lib/uglifier.rb:3:in `require' from /home/ritesh/.rvm/gems/ruby-1.9.3-p429/gems/uglifier-2.2.1/lib/uglifier.rb:3:in `<top (required)>' from /home/ritesh/.rvm/gems/ruby-1.9.3-p429@global/gems/bundler-1.3.5/lib/bundler/runtime.rb:72:in `require' from /home/ritesh/.rvm/gems/ruby-1.9.3-p429@global/gems/bundler-1.3.5/lib/bundler/runtime.rb:72:in `block (2 levels) in require' from /home/ritesh/.rvm/gems/ruby-1.9.3-p429@global/gems/bundler-1.3.5/lib/bundler/runtime.rb:70:in `each' from /home/ritesh/.rvm/gems/ruby-1.9.3-p429@global/gems/bundler-1.3.5/lib/bundler/runtime.rb:70:in `block in require' from /home/ritesh/.rvm/gems/ruby-1.9.3-p429@global/gems/bundler-1.3.5/lib/bundler/runtime.rb:59:in `each' from /home/ritesh/.rvm/gems/ruby-1.9.3-p429@global/gems/bundler-1.3.5/lib/bundler/runtime.rb:59:in `require' from /home/ritesh/.rvm/gems/ruby-1.9.3-p429@global/gems/bundler-1.3.5/lib/bundler.rb:132:in `require' from /home/ritesh/projects/interview/config/application.rb:7:in `<top (required)>' from /home/ritesh/.rvm/gems/ruby-1.9.3-p429/gems/railties-4.0.0/lib/rails/commands.rb:76:in `require' from /home/ritesh/.rvm/gems/ruby-1.9.3-p429/gems/railties-4.0.0/lib/rails/commands.rb:76:in `block in <top (required)>' from /home/ritesh/.rvm/gems/ruby-1.9.3-p429/gems/railties-4.0.0/lib/rails/commands.rb:73:in `tap' from /home/ritesh/.rvm/gems/ruby-1.9.3-p429/gems/railties-4.0.0/lib/rails/commands.rb:73:in `<top (required)>' from bin/rails:4:in `require' from bin/rails:4:in `<main>'
虽然我能够通过删除行gem之前的评论“therubyracer”,平台：：宝石从宝石文件修复它.
为什么当我们在启动rails应用程序时首先需要它的时候这个gem被注释掉了？
解决方法
因为如果在机器上安装了另一个JavaScript运行时(如Node.js),则Rails可以使用它,并且不需要therabyracer.
Rails使用ExecJS加载JavaScript运行时.有关ExecJS的更多信息,请参阅其Github页面：https://github.com/sstephenson/execjs.自述文件提供了可用的运行时间列表(作为错误日志说明).
根据您的部署过程和生产环境,您使用哪个JavaScript运行时可能并不重要.有些人对于therubyracer库的大小有问题(参见Rails – Could not find a JavaScript runtime?),并且在生产服务器上安装它可能并不聪明.