Ruby2js

Minimal yet extensible Ruby to JavaScript conversion.

Description

The base package maps Ruby syntax to JavaScript semantics. For example, a Ruby Hash literal becomes a JavaScript Object literal. Ruby symbols become JavaScript strings. Ruby method calls become JavaScript function calls IF there are either one or more arguments passed OR parenthesis are used, otherwise Ruby method calls become JavaScript property accesses. By default, methods, lambdas, and procs return undefined.

Ruby attribute accessors, methods defined with no parameters and no parenthesis, as well as setter method definitions, are mapped to Object.defineProperty, so avoid these if you wish to target users running IE8 or lower.

Filters may be provided to add Ruby-specific or framework specific behavior. Filters are essentially macro facilities that operate on an AST representation of the code.

See notimplemented_spec for a list of Ruby features known to be not implemented.

Synopsis

Basic:

require 'ruby2js'
puts Ruby2JS.convert("a={age:3}\na.age+=1")

With filter:

require 'ruby2js/filter/functions'
puts Ruby2JS.convert('"2A".to_i(16)')

Conversions can be explored interactively using the demo provided.

Introduction

JavaScript is a language where 0 is considered false, strings are immutable, and the behaviors for operators like == are, at best, convoluted.

Any attempt to bridge the semantics of Ruby and JavaScript will involve trade-offs. Consider the following expression:

a[-1]

Programmers who are familiar with Ruby will recognize that this returns the last element (or character) of an array (or string). However, the meaning is quite different if a is a Hash.

One way to resolve this is to change the way indexing operators are evaluated, and to provide a runtime library that adds properties to global JavaScript objects to handle this. This is the approach that Opal takes. It is a fine approach, with a number of benefits. It also has some notable drawbacks. For example, readability and compatibility with other frameworks.

Another approach is to simply accept JavaScript semantics for what they are. This would mean that negative indexes would return undefined for arrays and strings. This is the base approach provided by ruby2js.

A third approach would be to do static transformations on the source in order to address common usage patterns or idioms. These transformations can even be occasionally unsafe, as long as the transformations themselves are opt-in. ruby2js provides a number of such filters, including one that handles negative indexes when passed as a literal. As indicated above, this is unsafe in that it will do the wrong thing when it encounters a hash index which is expressed as a literal constant negative one. My experience is that such is rare enough to be safely ignored, but YMMV. More troublesome, this also won’t work when the index is not a literal (e.g., a[n]) and the index happens to be negative at runtime.

This quickly gets into gray areas. each in Ruby is a common method that facilitates iteration over arrays. forEach is the JavaScript equivalent. Mapping this is fine until you start using a framework like jQuery which provides a function named each.

Fortunately, Ruby provides ? and ! as legal suffixes for method names, Ruby2js filters do an exact match, so if you select a filter that maps each to forEach, each! will pass through the filter. The final code that emits JavaScript function calls and parameter accesses will strip off these suffixes.

Static transformations and runtime libraries aren't aren’t mutually exclusive. With enough of each, one could reproduce any functionality desired. Just be forewarned, that implementing a function like method_missing would require a lot of work.

Integrations

While this is a low level library suitable for DIY integration, one of the obvious uses of a tool that produces JavaScript is by web servers. Ruby2JS includes three such integrations:

As you might expect, CGI is a bit sluggish. By constrast, Sinatra and Rails are quite speedy as the bulk of the time is spend on the initial load of the required libraries.

Filters

In general, making use of a filter is as simple as requiring it. If multiple filters are selected, they will all be applied in parallel in one pass through the script.

  • strict adds 'use strict'; to the output

  • return adds return to the last expression in functions

  • functions

    • .all? becomes .every
    • .any? becomes .some
    • .chr becomes fromCharCode
    • .clear becomes .length = 0
    • .delete becomes delete target[arg]
    • .downcase becomes .toLowerCase
    • .each becomes forEach
    • .each_with_index becomes .forEach
    • .end_with? becomes .slice(-arg.length) == arg
    • .empty? becomes .length == 0
    • .first becomes [0]
    • .first(n) becomes .slice(0, n)
    • .gsub becomes replace //g
    • .include? becomes .indexOf() != -1
    • .keys becomes Object.keys()
    • .last becomes [*.length-1]
    • .last(n) becomes .slice(*.length-1, *.length)
    • .max becomes Math.max.apply(Math)
    • .min becomes Math.min.apply(Math)
    • .ord becomes charCodeAt(0)
    • puts becomes console.log
    • .replace becomes .length = 0; ...push.apply(*)
    • .start_with? becomes .substring(0, arg.length) == arg
    • .sub becomes .replace
    • .to_a becomes to_Array
    • .to_f becomes parseFloat
    • .to_i becomes parseInt
    • .to_s becomes .to_String
    • .upcase becomes .toUpperCase
    • [-n] becomes [*.length-n] for literal values of n
    • [n...m] becomes .slice(n,m)
    • [n..m] becomes .slice(n,m+1)
    • [/r/, n] becomes .match(/r/)[n]
    • .sub! and .gsub! become equivalent x = x.replace statements
    • .map!, .reverse!, and .select become equivalent .splice(0, .length, *.method()) statements
    • setInterval and setTimeout allow block to be treated as the first parameter on the call
    • for the following methods, if the block consists entirely of a simple expression (or ends with one), a return is added prior to the expression: sub, gsub, any?, all?, map.

  • underscore

    • .clone() becomes _.clone()
    • .compact() becomes _.compact()
    • .count_by {} becomes _.countBy {}
    • .find {} becomes _.find {}
    • .find_by() becomes _.findWhere()
    • .flatten() becomes _.flatten()
    • .group_by {} becomes _.groupBy {}
    • .has_key?() becomes _.has()
    • .index_by {} becomes _.indexBy {}
    • .invert() becomes _.invert()
    • .invoke(&:n) becomes _.invoke(, :n)
    • .map(&:n) becomes _.pluck(, :n)
    • .merge!() becomes _.extend()
    • .merge() becomes _.extend({}, )
    • .reduce {} becomes _.reduce {}
    • .reduce() becomes _.reduce()
    • .reject {} becomes _.reject {}
    • .sample() becomes _.sample()
    • .select {} becomes _.select {}
    • .shuffle() becomes _.shuffle()
    • .size() becomes _.size()
    • .sort() becomes _.sort_by(, _.identity)
    • .sort_by {} becomes _.sortBy {}
    • .times {} becomes _.times {}
    • .values() becomes _.values()
    • .where() becomes _.where()
    • .zip() becomes _.zip()
    • (n...m) becomes _.range(n, m)
    • (n..m) becomes _.range(n, m+1)
    • .compact!, .flatten!, shuffle!, reject!, sort_by!, and .uniq become equivalent .splice(0, .length, *.method()) statements
    • for the following methods, if the block consists entirely of a simple expression (or ends with one), a return is added prior to the expression: reduce, sort_by, group_by, index_by, count_by, find, select, reject.

  • jquery

    • maps Ruby unary operator ~ to jQuery $ function
    • maps Ruby attribute syntax to jquery attribute syntax
    • maps $$ to jQuery $ function
    • defaults the fourth parameter of $$.post to :jquery, allowing Ruby block syntax to be used for the success function.

  • angularrb

    • maps Ruby module to angular.module
    • maps filter, controller, factory, and directive to calls to angular module functions.
    • maps use statements to formal arguments or array values (as appropriate) depending on the module function.
    • maps watch statments to calls to $scope.$watch.
    • tracks globals variable and constant references and adds additional implicit use statements
    • maps constant assignments in an angular module to a filter
    • maps class definitions in an angular module to a filter
    • within a controller or within a link method in a directive:
      • maps apply, broadcast, digest, emit, eval, evalAsync, and parent calls to $scope functions.
      • maps apply!, broadcast!, digest!, eval!, and evalAsync! calls to $rootScope functions.
      • maps filter calls to '$filter` calls.
      • maps timeout and interval calls with a block to $timeout and $interval calls where the block is passed as the first parameter.

  • angular-route

    • maps case statements on $routeProvider to angular.js module configuration.
    • adds implicit module use of ngRoute when such a case statement is encountered

  • angular-resource

    • maps $resource.new statements on $resource function calls.
    • adds implicit module use of ngResource when $resource.new calls are encountered

Wunderbar includes additional demos:

Picking a Ruby to JS mapping tool

dsl — A domain specific language, where code is written in one language and errors are given in another. -- Devil’s Dictionary of Programming

If you simply want to get a job done, and would like a mature and tested framework, and only use one of the many integrations that Opal provides, then Opal is the way to go right now.

ruby2js is for those that want to produce JavaScript that looks like it wasn’t machine generated, and want the absolute bare minimum in terms of limitations as to what JavaScript can be produced.

Try for yourself. Compare.

And, of course, the right solution might be to use CoffeeScript instead.

License

(The MIT License)

Copyright (c) 2009, 2013 Macario Ortega, Sam Ruby

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.