When comparing Opa vs Nim, the Slant community recommends Nim for most people. In the question“What are the best languages that compile to JavaScript? ” Nim is ranked 3rd while Opa is ranked 30th. The most important reason people chose Nim is:
There are generics, templates, macros in Nim. They can allow you to write new DSL for your application, or avoid all boilerplate stuff.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Type Inferred
Opa uses type inference to decide what code runs on the client or the server, so you can organize code how you like, but still be sure that it runs where it needs to.
Pro Familiar Javascript Syntax
Opa's syntax is very similar to JavaScript, making it an easy choice for developers who are used to developing in JavaScript.
Pro Client and Server in the same language
Pro Great metaprogramming features
There are generics, templates, macros in Nim. They can allow you to write new DSL for your application, or avoid all boilerplate stuff.
Pro Strict typing
Checks your code at compile time.
Pro Has built-in unittest module
With built-in "unittest" module you can create test with a very readable code.
Pro Has built-in async support
Nim has "asyncdispatch" module, which allows you to write async applications.
Pro Compile-time execution
Nim has a built-in VM, which executes macros and some other code at compile time. For example, you can check if you're on Windows, and Nim will generate code only for it.
Pro Really cross-platform
The same code can be used for web, server, desktop and mobile.
Pro Easy to read
Nim has a lot of common with Python in terms of syntax. Indentation-based syntax, for/while loops.
Pro Multi paradigm
Imperative, OOP, functional programming in one language.
Pro Easy to integrate with another languages
You can use Nim with any language that can be interfaced with C. There's a tool which helps you to create new C and C++ bindings for Nim - c2nim.
Also, you can use Nim with Objective C or even JavaScript (if you're compiling for these backends).
Pro Garbage-collected
You don't need to deal with all those manual memory allocations, Nim can take care of it. But also you can use another GC, or tweak it for your real-time application or a game.
Pro Type interferencing
You only need to specify types in your procedures and objects - you don't need to specify type when you're creating a new variable (unless you're creating it without initialization).
Pro Built-in Unicode support
You can use unicode names for variables, there is "unicode" module for operations with unicode.
Pro Supports UFCS (Unified Function Call Syntax)
writeLine(stdout, "hello") can be written as stdout.writeLine("hello")
proc add(a: int): int = a + 5 can be used like 6.add.echo or 6.add().echo()
Cons
Con Not popular
Opa is not as popular as other languages which compile to JavaScript. Making it harder to find learning resources or even answers if you get stuck somewhere.