When comparing ClojureScript vs Erlang, the Slant community recommends ClojureScript for most people. In the question“What is the best programming language to learn first?” ClojureScript is ranked 41st while Erlang is ranked 44th. The most important reason people chose ClojureScript is:
Figwheel builds your ClojureScript code and hot loads it into the browser as you are coding! Every time you save your ClojureScript source file, the changes are sent to the browser so that you can see the effects of modifying your code in real time.
Specs
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Pros
Pro Live interactive programming with figwheel
Figwheel builds your ClojureScript code and hot loads it into the browser as you are coding! Every time you save your ClojureScript source file, the changes are sent to the browser so that you can see the effects of modifying your code in real time.
Pro Simple syntax
Lispness makes ClojureScript trivial to comprehend after an initial learning overhead.
Pro Easy to use existing JavaScript libraries
Clojure and ClojureScript are designed to be able to interact with their host. So the language by design makes it is easy to use existing JS libraries.
Pro Targets Google Closure-ready JavaScript for immense optimizations
Google's Closure Library converts regular JavaScript into a highly optimized form - including dead code analysis/elimination. It can even remove pieces of unused code from 3rd party libraries (eg, if you import jQuery but only use one function, Google Closure includes only that piece).
Pro Share application logic between browser and Clojure server
Clojure is also able to run web servers, so one can reap similar benefits to NodeJS in terms of sharing code between client and server.
Pro Can be used with React out of the box
Pro Excellent build tools
Both Leiningen and Boot are great build tools that manage code dependencies and deployment.
Pro Excellent tools for web development
ClojureScript has superb wrappers around React.js (see Reagent) that make building single-page apps a breeze. With figwheel, it's a web dev experience unlike any other -- hotloaded code, repl interaction, and instantly reflected changes make good development fun and fast. You can add things like Garden to make CSS-writing part of the same holistic experience and suddenly all development is a pleasant, smooth process.
Pro The Spec core library
From the creator of Clojure:
Spec is a new core library (Clojure 1.9 and Clojurescript) to support data and function specifications in Clojure.
Writing a spec should enable automatic: Validation, Error reporting, Destructuring, Instrumentation, Test-data generation and Generative test generation.
Pro Built from the ground up with concurrency and distributed computing in mind
Erlang has strong roots with the telecom industry in which concurrent processes are normal. It's designed to be concurrent, to be used for distributed computing and to be scalable.
Pro Fault-tolerant
Fault tolerance means that a system has the property to continue operating even though one or more components have failed.
For Erlang systems, this means that the system is kept running even if for example a user has to drop a phone call rather than forcing everyone else to do so.
In order to achieve this, Erlang's VM gives you:
- Knowledge of when a process died and why that happened
- The ability to force processes to die together if they depend on each other and if one of them has a fault.
- A logger that logs every uncaught exception
- Nodes that can be monitored so that you find out when they go down
- The ability to restart failed processes (or groups of them)
Pro Upgrade code without stopping the system
In a real-time system it may not be possible to stop the system in order to implement code upgrades. For these cases Erlang gives you dynamic code upgrade support for free when using OTP. The mechanism is very easy to understand and works as follows:
- Start the app
- Edit the code
- Recompile
That's all that is needed, the app updates with the new code while it's still running and tests are run automatically.
Pro Great for writing distributed applications
Erlang is made to be parallel and distributed. Because it's very easy to write code that uses multiple processor cores, it's also very easy to write applications that span multiple servers.
Pro Battle proven
Erlang has been used in production for more than 20 years now. During that time it has proven itself over and over again that works great in both small startups and large-scale enterprise systems.
Erlang has been used extensively by Ericsson themselves. For example, the AXD301 ATM, which is one of Ericsson's flagships is probably the largest Erlang project ever with more than 1.1 million lines of Erlang code.
Pro Light processes
Erlang's processes have very little overhead (about 500 bytes per process). This means that a huge amount of processes can be created, even on older machines.
Pro Consistency across platforms
Erlang's processes run in a complete independent way from the OS (they aren't managed by the OS scheduler neither). This means that programs written in Erlang will run exactly the same way regardless of the operating system or platform.
Cons
Con Tooling is horrible
I've never seen worse tooling before. Writing tests and getting test coverage reports is near impossible. Tooling is brittle and clunky. Feels prehistoric.
Con Syntax may seem cryptic to people not used to Lisp
Lisp is sometimes called "syntax-less" and this is bewildering to those steeped in Algol-type syntax (Java, Javascript, C, etc). Being a dialect of Lisp, ClojureScript's syntax may seem cryptic and hard to understand for people not used to it. While Lisp has very little syntax compared to other languages and it's generally considered pretty terse, there's still an initial overhead in learning the language.
Con Eccentric syntax
Erlang's syntax may feel very strange to 99% of programmers who have never used it. This is because it does not share any similarities or common syntax definitions that are found in all the other languages that are used today.
Con Useful in only one niche
Erlang is not really a general purpose language. It has a very special and well-defined niche where it towers above everything else. It's specialized in scalability and in distributed applications. Which is not necessarily a bad thing per se, but it still lacks and falls behind other languages when it needs to do things outside it's niche.