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Pro Concise syntax
F#'s syntax tends to be terse while remaining very readable and easy to understand without being a chore to write.
Pro Easier transition from other paradigms
Since F# is not a purely functional language, it lends itself to being more easily picked up by programmers that have experience with other paradigms.
Pro .NET Interoperability
Since F# runs on the Common Language Runtime or CLR, it has access to the entire .NET Framework, as well as libraries written in other .NET languages such as C#, VB.NET, and C++/CLI.
Pro Multiplatform, it runs on .Net Core
Forget Xamarin and Mono. F# now runs on the multiplatform .Net Core!
Pro Natively supported by Visual Studio
This is a .Net language natively supported by Visual Studio. Though it is not as tooled up as C# the support is still substantial. In particular, C# deployment scenarios can be enabled for it with small C# wrapper projects. Integration with Visual Studio provides: IntelliSense, debugging, projects an other features.
Pro You can run F# in the browser
Pro Fall into the pit of success
F# directs you into a workflow where the right way is the path of least resistance.
Coming from a C# background, its restrictions might feel arbitrary at first (e.g., what do you mean my code has to be in dependency order!? Arbitrary alphabetical or bust!), but you'll soon realize that your code is cohesive, concise and consistent in a way that it never was before - and you can compile and run with confidence!
Pro F# is supported by Xamarin
Thanks to Xamarin, F# is a functional language that you can use to build for iOS, Android and Windows.
Pro Required for web development
Pro No installation required
Pro First-class functions with lexical closures
Pro Runs on both the browser and the server
Pro Instant gratification
Pro C-like syntax
Pro Easy to build an application
By using the UI capabilities in HTML and CSS you can develop substantial applications with graphical interfaces more quickly and with less effort than in other languages which would require you to learn a windowing library.
Building a useful application is one of the best ways to learn a new language and because of the low learning curve for creating applications you can create more substatial programs and learn more practical programming priciple faster.
Pro JSON is native to JS
JSON is arguably a "must-learn". With JS, that's one less additional syntax to learn.
Pro Massive ecosystem
Pro Great tools for development
Flow, JSHint/ESLint, Babel, npm, etc.
Pro Can be very simple (teachable)
By setting a few ground-rules (effectively coding in a subset of JS), JS is one of the simplest languages to learn (requiring very few must-learn prerequisite concepts).
Pro Very good debugger
Has a built in debugger with break points, watches that work on local values, and a console that you can use to edit anything at any time. Both in the browser (eg: Chrome), and server (eg: Nodejs).
Pro Complete dev stack can be run online
Pro Speed (most implementations)
JS/ES is in the running for the fastest interpreted language given the optimizations and JIT integration of popular implementations. On the other hand, it fails utterly when compared with compiled (to native or VM code) languages.
Pro Several Platforms to use the web stack and JS to create multi-platform apps
Opens the door to native application development as well as just websites. Use with React Native, Weex or Quasar (Vue), PhoneGap or Cordova, NativeScript... (etc) to build native apps. Use mostly the same code base for multi-platform and web.
May also be a con.
Pro Modern ESNext is far better than the JS of days past
Modern JS has made great strides, and can be targerted to older (or non-standard) browsers using Babel. There are new language constructs that can make programming in JS comfortable.; e.g.: async / await ( <3 ).
Pro Prototype based Object Oriented System
For example, in a prototypical language, you think of a rectangle, and define it. You now have a rectangle. Let's say you want a red rectangle, you copy the rectangle and give it the property red. Want a blue one? Copy rectangle again give it a blue. Big blue rectangle? Copy blue rectangle and make it big. In a class-based language, first you describe a rectangle, describe a red rectangle as a type of rectangle, describe blue and big blue rectangles, and now that you have described them, you must create instances of them, and only then do you have the rectangles. Essentially: Classes are factories for objects, prototypes are objects themselves, and the latter method was created to be more intuitive, which is particularly advantageous to beginners.
Pro Integrates very well with UE4
Coding an immersive 3D game can retain the attention of new programmers. ncsoft/Unreal.js.
Pro Extremely popular
Pro The most used language in the whole Solar System in amount of scripts/applications
Because it runs in many different environments, it is the most used language in the world.
Con Has no ad-hoc polymorphism (á la Type Classes)
You have generics, you have interfaces, you have inheritance, you have a lot of things at your disposal but you don't have Type Clases. They can be emulated using some clever constructs but there's nothing like having the real thing.
Con Many errors pass silently
Con Easy to accidentally use globals
If you forget a
Con The "this" keyword doesn't mean what you think it means
this is bound to whatever object called the function. Unless you invoke it as a method. Unless you invoke it as a constructor. Unless it's an arrow function.
Con Weird type coercions
'5' - 1 == 4, but
'5' + 1 == 51. There are other examples that make even less sense.
Con Each browser has its own quirks when executing the same code in some cases
Beginner programmers often make the mistake of coding something, seeing it works in the browser they tested it in, and then scratching their heads when it doesn't work in another browser. Ideally you'd want a language that works consistently across all platforms in order to be able to focus more on the programming and less on the underlying environment. It just takes time away from learning and forces you to spend time figuring out why this worked in browser X but not browser Y.
Con Easy to fall into bad manners and bad mind structure
It wouldn't consolidate a good mind structure for moving to other languages. Too open.
Con Does not teach you about data types
Con Limited standard library
Much often needed functionality is not in the standard library. (Contrast with Python.) However, there are well established libraries such as Lodash, to fill the gap (however, due to the diverse/fractured ecosystem it may not be clear what library to use).
Con The constant churn of tooling and language
Con Many tutorials, code, and resources, are structured for older ES5 code
Con Asynchronous coding is not easy for beginners
Con The `null` and `undefined` objects aren't really objects
Therefore, attempts to call methods on them will fail. This is especially frustrating since these are often returned instead of throwing exceptions. So a failure may appear far away from the actual cause, which makes bugs very hard to find.
Con Array-like objects
Many cases when you should get an Array, you just get an Array-like object instead and none of the Array methods work on it.
Con Fast moving
The language and the web platform move fast these days. this makes it difficult for students as there is a lot of fragmentation and outdated information.
Con Numbers that begin with 0 are assumed octal
This is very surprising for beginners. Especially since
07 seem to work just fine. And this isn't just for hardcoded numbers. The
parseInt() function has the same problem, but only on some systems.
Con Good tools are pretty much a MUST for new programmers
You really want to be using a good editor (light IDE) and a linter, type checker (e.g.:Flow), etc. until you grok the language. And choosing / setting-up that development environment is it's own learning curve. If taught in a classroom, using a subset of JS with solid tools, there is an argument that JS could be an ideal first language... however, that is a lot of ceremony to protect the new programmer from JS gotchas. But without the tools, JS can be a very painful painful first language (trying to figure out why your code isn't doing what you intended).
Con Very confusing to read
Con Has really bad parts you're better off avoiding altogether
Con Counter-intuitive type conversion
3+5; // 8; "Hello "+"world"; // "Hello world"
+ with a string and a non-string operand, the non-string operand is converted to a string and the result is concatenated:
"the answer is "+42; // "the answer is 42" "this is "+true; // "this is true"
In any other case (except for Date) the operands are converted to numbers and the results are added:
1+true; // = 1+1 = 2; null+false; // = 0+0 = 0;
Con Fractured ecosystem
Angular, React, Ember, Meteor, Backbone, Knockout, Express, Mithril, Aurelia. The web frameworks pass in and out of fashion too quickly to keep up with. The endless civil wars are becoming tiresome.