Parse a JS file using JRuby and Rhino and print the AST

rhino_ast.rb

require 'js-1_7r3.jar'

import Java::OrgMozillaJavascript::Context
import Java::OrgMozillaJavascript::CompilerEnvirons
import Java::OrgMozillaJavascript::Parser
import Java::OrgMozillaJavascript::Token

class Visitor
  include Java::OrgMozillaJavascriptAst::NodeVisitor
  
  def visit(node)
    indent = "  " * node.depth
    type_name = Token.type_to_name(node.type)
    name = case node.type
    when Token::NAME
      node.identifier
    when Token::COMMENT, Token::NUMBER, Token::REGEXP, Token::STRING
      node.to_source
    end
    puts [node.lineno, indent, type_name, name].join('  ')
    true
  end
end

context = Context.enter()
context.init_standard_objects()
compiler_environs = CompilerEnvirons.new
compiler_environs.init_from_context(context)
parser = Parser.new(compiler_environs, nil)

script = "
/// This is a test.
function foo() {
  alert('Hello, world!');
}
"
ast = parser.parse(script, '<code>', 1)
ast.visit(Visitor.new);

=begin
$ jruby rhino_ast.rb
1    SCRIPT  
2      COMMENT  /// This is a test.
3      FUNCTION  
3        NAME  foo
3        BLOCK  
4          EXPR_VOID  
4            CALL  
4              NAME  alert
4              STRING  'Hello, world!'
=end