Odd thing happened:

gxg_bootstrap.rb:
_____________________________________________________________
# Require Core Library:
require 'opal/full'
# Require Standard Library:
require 'benchmark'
require 'bigdecimal'
require 'buffer'
require 'base64'
require 'console'
require 'date'
require 'delegate'
require 'encoding'
require 'enumerator'
require 'erb'
require 'fileutils'
require 'forwardable'
require 'iconv'
require 'json'
require 'js'
require 'observer'
require 'opal-parser'
require 'opal-platform'
require 'ostruct'
require 'pathname'
require 'pp'
require 'promise'
require 'securerandom'
require 'set'
require 'singleton'
require 'stringio'
require 'strscan'
require 'template'
require 'thread'
require 'time'
# opal-browser Integration:
require 'opal-browser'

Compile command:
_______________________________________________________________
opal --gem paggio --gem opal-browser --compile gxg_bootstrap.rb > ../lib/public/external/gxg_bootstrap.js

In-Browser Error:
_______________________________________________________________
gxg_bootstrap.js:20687 DEPRECATION: encoding is now part of the core library, requiring it is deprecated

$writer @ gxg_bootstrap.js:20687
write @ gxg_bootstrap.js:20575
puts @ gxg_bootstrap.js:20632
Opal.send @ gxg_bootstrap.js:1605
warn @ gxg_bootstrap.js:4981
Opal.modules.encoding @ gxg_bootstrap.js:26222
Opal.load @ gxg_bootstrap.js:2192
Opal.require @ gxg_bootstrap.js:2216
(anonymous) @ gxg_bootstrap.js:56116
(anonymous) @ gxg_bootstrap.js:56140
gxg_bootstrap.js:20687 Object freezing is not supported by Opal

$writer @ gxg_bootstrap.js:20687
write @ gxg_bootstrap.js:20575
puts @ gxg_bootstrap.js:20632
Opal.send @ gxg_bootstrap.js:1605
warn @ gxg_bootstrap.js:4981
warn @ gxg_bootstrap.js:21334
handle_unsupported_feature @ gxg_bootstrap.js:21321
freeze @ gxg_bootstrap.js:21465
(anonymous) @ gxg_bootstrap.js:28388
Opal.modules.parser/messages @ gxg_bootstrap.js:28389
Opal.load @ gxg_bootstrap.js:2192
Opal.require @ gxg_bootstrap.js:2216
(anonymous) @ gxg_bootstrap.js:41115
Opal.modules.parser @ gxg_bootstrap.js:41180
Opal.load @ gxg_bootstrap.js:2192
Opal.require @ gxg_bootstrap.js:2216
Opal.modules.parser/ruby23 @ gxg_bootstrap.js:41196
Opal.load @ gxg_bootstrap.js:2192
Opal.require @ gxg_bootstrap.js:2216
Opal.modules.opal/ast/builder @ gxg_bootstrap.js:44900
Opal.load @ gxg_bootstrap.js:2192
Opal.require @ gxg_bootstrap.js:2216
Opal.modules.opal/parser @ gxg_bootstrap.js:46007
Opal.load @ gxg_bootstrap.js:2192
Opal.require @ gxg_bootstrap.js:2216
Opal.modules.opal/compiler @ gxg_bootstrap.js:53541
Opal.load @ gxg_bootstrap.js:2192
Opal.require @ gxg_bootstrap.js:2216
Opal.modules.opal-parser @ gxg_bootstrap.js:54063
Opal.load @ gxg_bootstrap.js:2192
Opal.require @ gxg_bootstrap.js:2216
(anonymous) @ gxg_bootstrap.js:56125
(anonymous) @ gxg_bootstrap.js:56140
gxg_bootstrap.js:5022 Uncaught $NoMethodError {name: "append_path", message: "undefined method `append_path' for Opal", args: Array(1), stack: "append_path: undefined method `append_path' for Opal"}
raise @ gxg_bootstrap.js:5022
method_missing @ gxg_bootstrap.js:3741
method_missing_stub @ gxg_bootstrap.js:1197
Opal.modules.opal/browser @ gxg_bootstrap.js:56090
Opal.load @ gxg_bootstrap.js:2192
Opal.require @ gxg_bootstrap.js:2216
Opal.modules.opal-browser @ gxg_bootstrap.js:56099
Opal.load @ gxg_bootstrap.js:2192
Opal.require @ gxg_bootstrap.js:2216
(anonymous) @ gxg_bootstrap.js:56139
(anonymous) @ gxg_bootstrap.js:56140