# File lib/execjs/runtimes.rb, line 55 def self.from_environment if name = ENV["EXECJS_RUNTIME"] if runtime = const_get(name) if runtime.available? runtime if runtime.available? else raise RuntimeUnavailable, "#{runtime.name} runtime is not available on this system" end elsif !name.empty? raise RuntimeUnavailable, "#{name} runtime is not defined" end end end