When comparing PharoJS vs Reason ML, the Slant community recommends Reason ML for most people. In the question“What are the best languages that compile to JavaScript? ” Reason ML is ranked 10th while PharoJS is ranked 13th.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Program the web in Smalltalk
For people who enjoy programming in Smalltalk, Pharo allows developers to use Smalltalk for web development as well, since it transpiles Smalltalk code to JavaScript.
Pro Support for Phonegap to go directly to iOS/Android mobile App
Pro Compiles to very efficient Javascript, with almost perfect Smalltalk semantics
Pro Great IDE support
Pro Seamless integration with JavaScript libraries
Can directly call to / be called from JavaScript and can use foreign JavaScript objects.
Will soon have ability to generate and use AMD modules.
Pro Uses the excellent Bucklescript Ocaml to Javascript transpiler
Pro Superior type inference
Ocaml type inference is so smart that you never have to repeat yourself and keep code very clean, type errors also are very pleasant.
Pro Aims to make the transition from Javascript easier
Despite being a completely different language Javascript programmer will find that the syntax of ReasonML has many familiarities with Javascript.
Pro Uses established compiler technology from Ocaml with a tweaked syntax that leans more towards Javascript
Pro Removes JavaScript "bad parts" but sticks to it's design philosophy
unlike other js-targetting languages that are thought as a way to have a language that pleases community X run in a browser, reason is really designed with JavaScript community in mind. it removes the bad parts but keeps its syntax and its best design principles (from Scheme): simplicity, minimalism, and functions as building block.
Pro Immutability with escape hatches
reason includes true immutability, but it has escape hatches to let you use mutations in exceptional cases.
Pro Compiles to JavaScript or assembly (ocaml)
The same reasonml code can compile to js (eg. run on browsers or node.js, use any lib in npm), or compile to assembly thru ocaml (unless of course you load js externals), running on any device, with C-comparable (or better) performance.
Pro JSX syntax natively supported
Reason was created by the creator of react, for developers already using JSX to template web or native UIs this results very familiar.
Cons
Con A standard async syntax is pending
Async syntax is not standard across native/js projects and in both cases a bit awkward for non-ocaml devs. Currently this is reasonml most voted issue in their GitHub repo so hopefully, there's news soon.
Con Ecosystem is a mess
A wonderful language, but a user is required to use multiple different package managers for many things (esy, bsb, npm). Some standard templates from bsb (e.g. react-starter) are not installable out of the box.