尝试加载gem'uglifier'时出错。（捆绑器:: GemRequireError）

为什么会出现此错误？

shibly@mybox:~/blog$ rails server
/home/shibly/.gem/ruby/2.2.4/gems/bundler-1.11.2/lib/bundler/runtime.rb:80:in `rescue in block (2 levels) in require': There was an error while trying to load the gem 'uglifier'. (Bundler::GemRequireError)
    from /home/shibly/.gem/ruby/2.2.4/gems/bundler-1.11.2/lib/bundler/runtime.rb:76:in `block (2 levels) in require'
    from /home/shibly/.gem/ruby/2.2.4/gems/bundler-1.11.2/lib/bundler/runtime.rb:72:in `each'
    from /home/shibly/.gem/ruby/2.2.4/gems/bundler-1.11.2/lib/bundler/runtime.rb:72:in `block in require'
    from /home/shibly/.gem/ruby/2.2.4/gems/bundler-1.11.2/lib/bundler/runtime.rb:61:in `each'
    from /home/shibly/.gem/ruby/2.2.4/gems/bundler-1.11.2/lib/bundler/runtime.rb:61:in `require'
    from /home/shibly/.gem/ruby/2.2.4/gems/bundler-1.11.2/lib/bundler.rb:99:in `require'
    from /home/shibly/blog/config/application.rb:7:in `<top (required)>'
    from /home/shibly/.gem/ruby/2.2.4/gems/railties-4.2.5/lib/rails/commands/commands_tasks.rb:78:in `require'
    from /home/shibly/.gem/ruby/2.2.4/gems/railties-4.2.5/lib/rails/commands/commands_tasks.rb:78:in `block in server'
    from /home/shibly/.gem/ruby/2.2.4/gems/railties-4.2.5/lib/rails/commands/commands_tasks.rb:75:in `tap'
    from /home/shibly/.gem/ruby/2.2.4/gems/railties-4.2.5/lib/rails/commands/commands_tasks.rb:75:in `server'
    from /home/shibly/.gem/ruby/2.2.4/gems/railties-4.2.5/lib/rails/commands/commands_tasks.rb:39:in `run_command!'
    from /home/shibly/.gem/ruby/2.2.4/gems/railties-4.2.5/lib/rails/commands.rb:17:in `<top (required)>'
    from bin/rails:9:in `require'
    from bin/rails:9:in `<main>

您应该运行以下命令在Ubuntu中安装NodeJS

sudo apt-get install nodejs

或在OSX上运行

brew install nodejs

Uglifier是一个JS包装器，它需要运行JS运行时或JS解释器。我会选择安装NodeJS。

在默认的Rails Gemfile中，注释掉宝石'therubyracer'的行。如果您取消注释，则将获得该宝石，它应该可以工作。

从“ Rails入门 ”：

编译CoffeeScript和JavaScript资产压缩要求您的系统上有一个JavaScript运行时，如果没有运行时，则会execjs在资产编译期间看到错误。通常，Mac OS X和Windows都装有JavaScript运行时。Rails将therubyracer宝石添加到生成Gemfile的新应用程序的注释行中，您可以在需要时取消注释。therubyrhino是JRuby用户推荐的运行时，默认情况下添加到GemfileJRuby下生成的in应用程序中。您可以在ExecJS上研究所有受支持的运行时。

创建数据库时出错。

问题是Node.js尝试sudo在脚本中不安装以下内容：

sudo apt-get install nodejs