为什么gem`therubyracer`默认在Gemfile中注释掉了？
我创建了一个rails应用程序，并尝试启动rails服务器。 我收到了以下错误：
/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 `' from /home/ritesh/.rvm/gems/ruby-1.9.3-p429/gems/execjs-2.0.1/lib/execjs.rb:4:in `' 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 `' 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 `' 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 ' 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 `' from bin/rails:4:in `require' from bin/rails:4:in `' 虽然我能够通过删除行gem 'therubyracer', platforms: :ruby之前的注释来修复它gem 'therubyracer', platforms: :ruby来自Gemfile gem 'therubyracer', platforms: :ruby 。
当我们在启动rails应用程序时首先需要它时，为什么这个gem被注释掉了？
因为如果在机器上安装了另一个JavaScript运行时（如Node.js），Rails可以使用它，并且不需要therubyracer。
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运行时列表（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therubyracer库的大小有疑问（请参阅Rails – 找不到JavaScript运行时？ ），在生产服务器上安装它可能并不聪明。