When comparing Haskell (via GHCJS) vs PharoJS, the Slant community recommends PharoJS for most people. In the question“What are the best languages that compile to JavaScript? ” PharoJS is ranked 13th while Haskell (via GHCJS) is ranked 28th. The most important reason people chose PharoJS is:
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.
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Pros
Pro Terse
Haskell is a very terse language, particularly due to its type inference. This means there's nothing to distract from the intent of the code, making it very readable. This is in sharp contrast to languages like Java, where skimming code requires learning which details can be ignored. Haskell's terseness also lends itself to very clear inline examples in textbooks, and makes it a pleasure to read through code even on a cellphone screen.
Pro Quick Feedback
It's often said that, in Haskell, if it compiles, it works. This short feedback loop can speed up learning process, by making it clear exactly when and where mistakes are made.
Pro All of Haskell, with the same tools you're used to
No need to learn new syntax or semantics, and no need to install and learn a bunch of new tools - it's just GHC.
Pro Provides seamless concurrency, without the need for promises or callbacks
Pro Built-in REPL which lets you interact with your GHCJS compiled web page
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.
Cons
Con The generated code can be difficult to debug
It should be mentioned that since the execution model of Haskell is very different from common imperative languages (lazy evaluation), the generated code doesn't resemble the source code at all, so it can be very difficult to debug.
Con Large runtime
GHCJS supports the entire Haskell runtime, the Javascript it outputs tends to be quite large. This is in contrast to options such as Fay, which save some overhead by not supporting some features such as multi-threading.