Added

• Basic support for uplevel: keyword argument in Kernel#warn (#2006)
• Added a #respond_to_missing? implementation for BasicObject, Delegator, OpenStruct, that's meant for future support in the Opal runtime, which currently ignores it (#2007)
• Opal::Compiler#magic_comments that allows to access magic-comments format and converts it to a hash (#2038)
• Use magic-comments to declare helpers required by the file (#2038)
• Opal.$$ is now a shortcut for Opal.const_get_relative (#2038)
• Opal.$$$ is now a shortcut for Opal.const_get_qualified (#2038)
• Added support for globalThis as the generic global object accessor (#2047)
• Opal::Compiler#magic_comments that allows to access magic-comments format and converts it to a hash
• Use magic-comments to declare helpers required by the file
• Opal.$$ is now a shortcut for Opal.const_get_relative
• Opal.$$$ is now a shortcut for Opal.const_get_qualified
• Source-map support for Node.js in the default runner (#2045)
• SecureRandom#hex(n) (#2050)
• Added a generic implementation of Kernel#caller and #warn(uplevel:) that works with sourcemaps in Node.js and Chrome (#2065)
• Added support for numblocks -> { _1 + _2 }.call(3, 4) # => 7 (#2149)
• Support <internal:…> and <js:…> in stacktraces, like MRI we now distinguish internal lines from lib/app lines (#2154)
• Array#difference, Array#intersection, Array#union as aliases respectively to Array#{-,&,|} (#2151)
• Aliases filter{,!} to select{,!} throughout the corelib classes (#2151)
• Enumerable#filter_map, Enumerable#tally (#2151)
• Alias Kernel#then for Kernel#yield_self (#2151)
• Method chaining: {Proc,Method}#{<<,>>} (#2151)
• Added Integer#to_d (#2006)
• Added a compiler option use_strict which can also be set by the use_strict magic comment (#1959)
• Add --rbrequire (-q) option to opal command line executable (#2120)

Fixed

• Array#delete_if (#2069)
• Array#keep_if (#2069)
• Array#reject! (#2069)
• Array#select! (#2069)
• Struct#dup (#1995)
• Integer#gcdlcm (#1972)
• Enumerable#to_h (#1979)
• Enumerator#size (#1980)
• Enumerable#min (#1982)
• Enumerable#min_by (#1985)
• Enumerable#max_by (#1985)
• Set#intersect? (#1988)
• Set#disjoint? (#1988)
• Set#keep_if (#1987)
• Set#select! (#1987)
• Set#reject! (#1987)
• String#unicode_normalize (#2175)
• Module#alias_method (#1983)
• Enumerable#minmax_by (#1981)
• Enumerator#each_with_index (#1990)
• Range#== (#1992)
• Range#each (#1991)
• Enumerable#zip (#1986)
• String#getbyte (#2141)
• Struct#dup not copying $$data (#1995)
• Fixed usage of semicolon in single-line backticks (#2004)
• Module#attr with multiple arguments (#2003)
• PathReader used to try to read missing files instead of respecting the missing_require_severity configuration value (#2044)
• Removed some unused variables from the runtime (#2052)
• Fixed a typo in the runtime (#2054)
• Fix Regexp interpolation, previously interpolating with other regexps was broken (#2062)
• Set match on StringScanner#skip and StringScanner#scan_until (#2061)
• Fix ruby 2.7 warnings (#2071)
• Improve the --help descriptions (#2146)
• Remove BasicObject#class (#2166)
• Time#strftime %j leading zeros (#2161)
• Fix call { true or next } producing invalid code (#2160)
• define_method can now be called on the main object (#2029)
• Fix nested for-loops (#2033)
• Fix Number#round for Integers (#2030)
• Fix parsing Unicode characters from Opal (#2073)
• Integer#===: improve Integer recognition (#2089)
• Regexp: ensure ignoreCase is never undefined (#2098)
• Hash#delete: ensure String keys are converted to values (#2106)
• Array#shift: improve performance on v8 >7.1 (#2115)
• Array#pop(1): improve performance (#2130)
• Object#pretty_inspect (#2139)
• Fix conversion from UTF-8 to bytes (#2138)
• Restore compatibility with Chrome 38, used by Cordova and many mobile browsers (#2109)

Changed

• Updated outdated parser version (#2013)
• Nashorn has been deprecated but GraalVM still supports it (#1997)
• "opal/mini" now includes "opal/io" (#2002)
• Regexps assigned to constants are now frozen (#2007)
• Opal.$$ changed from being the constant cache of Object to being a shortcut for Opal.const_get_relative (#2038)
• Moved REPL implementation from bin/ to its own lib/ file as opal/repl.rb (#2048)
• Encoding.default_external is now initialized with __ENCODING__ (#2072)
• Keep the MersenneTwister implementation private (#2108)
• Change parser to 3.0 (#2148)
• Fix forwarding a rescued error to a global var: rescue => $gvar (#2154)
• Now using Parser v3.0 and targeting Ruby 3.0 (#2156)
• Comparable#clamp to support a Range argument (#2151)
• #to_h method to support a block (shortform for .map(&block).to_h) (#2151)
• BigDecimal is now a subclass of Numeric (#2006)
• PP to be rebased on upstream Ruby version (#2083)
• String to report UTF-8 encoding by default, as MRI does (#2117)
• Don't output "Failed to load WithCLexer, using pure Ruby lexer" warning unless in $DEBUG mode (#2174)

Deprecated

• Requiring nodejs/stacktrace has been deprecated, source-maps are already
  supported by the default Node.js runner or by requiring https://github.com/evanw/node-source-map-support
  before loading code compiled by Opal (#2045)

Removed

• Removed special compilation for the Opal.truthy? and Opal.falsy? helpers (#2076)
• Removed the deprecated tainting compiler config option (#2072)