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.

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. It’s 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 passes 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]) where 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.

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

Picking a Ruby to JS mapping tool

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 with the absolute bare minimum in terms of limitations as to what JavaScript can be produced.

Try for yourself. Compare.

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.