When comparing Elm vs Riot, the Slant community recommends Elm for most people. In the question“What are the best React.js alternatives?” Elm is ranked 1st while Riot is ranked 4th. The most important reason people chose Elm is:
Lack of run-time exceptions makes it easy to produce large swathes of reliable front-end code without drowning in tests.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro No run-time exceptions
Lack of run-time exceptions makes it easy to produce large swathes of reliable front-end code without drowning in tests.
Pro Inferred static typing
ML static typing is great because it's always there, you just choose how explicit you want to be and how much you want the compiler to do.
Pro Super easy refactoring with very helpful compiler errors
In no other language you can refactor so easy without any worries, since the compiler will guide you through. It is like TDD but than compiler-error driven.
Pro Designed around high-level front-end development
As Elm was designed as a front-end langauge, it has out of the box support for things like DOM-element creation, letting programmers focus on their application logic, rather than implementation details specific to the web.
Pro Great and simple way to learn Purely Functional Programming
You can try to apply some functional programming ideas in other languages that have an imperative basis, but you haven't seen the real power unless you tried it in the environment of purely functional programming. Elm is a simple language with great learning resources and easy graphical output, which makes it easy to explore the power of functional programming. Plus programming in Elm is very readable.
Pro Good tooling
All major editors have great support. With Atom for example, Elm plugins are available for linting, formatting, make/compiler support and Elmjutsu will simply overflow you with super useful functions, like navigate to referenced definition and show expression type.
Pro Batteries included
The Elm Architecture means you don't need to spend valuable time and effort choosing the right frameworks, state management libraries, or build tooling. It's all built in.
Pro Static module system
Elm uses easy to use modules.
Use:
import List
import List as L
import List exposing (..)
import List exposing ( map, foldl )
import Maybe exposing ( Maybe )
import Maybe exposing ( Maybe(..) )
import Maybe exposing ( Maybe(Just) )
Creation:
module MyModule exposing (foo, bar)
Pro Missing syntactic sugar
Easy to learn, most functions have only one way, not 5 alternatives where you must study where to best use what.
Pro Growing community
Pro Interactive Programming and Hot Swapping
Support for hot swapping and interactive programming is included.
Pro Easy to code review
The lack of side-effects and simple, consistent language semantics make it easy to quickly review incoming changes.
Pro Higher confidence in code correctness and quality
Pure functions, immutable data structures, amazing compiler, clean and homologous syntax used for HTML, logic, and optionally to replace CSS, elimination of entire classes of bugs so you don't even need most unit tests. These factors lead to better code, better programs, higher confidence, and ultimately, more satisfaction.
Pro Not quite Haskell semantics
Luckily you do not have to learn Haskell to be able to do any Elm. It is meant to be a language that compiles to Javascript, so for Javascript programmers (Front end) not for CS students who want to learn as many different algorithms as possible.
Pro Minimal DOM operations
Riot takes the expressions from a DOM tree and stores them in an array. Each of these expressions points to a DOM node. On each cycle these expressions are compared to the values in the DOM. So when a value has changed, Riot automatically updates the corresponding node. This way the operations are kept to a minimal amount and since the expressions can be cached, going through 1000 of them takes less than 1ms.
Pro Lightweight
Riot is made to be used with websites of any kind, so it's built to be easy and lightweight, but still maintaining all the needed features for a UI library. It's only 2.5 KB in size when minified. So it can also be used for mobile web apps without requiring much bandwidth to download.
Pro Components use familiar HTML tags
Riot components use custom tags which are nothing more than familiar HTML tags coupled with JavaScript. This eliminates the need to learn another templating language or syntax. For example:
<todo>
<h3>TODO</h3>
<ul>
<li each={ item, i in items }>{ item }</li>
</ul>
<form onsubmit={ handleSubmit }>
<input>
<button>Add #{ items.length + 1 }</button>
</form>
this.items = []
handleSubmit(e) {
var input = e.target[0]
this.items.push(input.value)
input.value = ''
}
</todo>
Riot tries to separate HTML and JavaScript, while still keeping them inside the component. This way, the HTML can also be neatly mixed with JavaScript expressions.
Pro Supports server side rendering
Riot has support for server side rendering. The views and data are rendered on the server, then those views are sent as HTML to the browser when a user requests them.
This helps with initial loading time and is very useful for SEO purposes because the web app is indexed by search engines same as other static websites that have their HTML on the server.
Pro Easily pluggable with JS/HTML/CSS preprocessors
It is very easy to use your favorite preprocessors with the Riot compiler. Riot comes with CoffeeScript, ES6 (Babel), TypeScript, LiveScript and Jade support. You can also add your own parsers.
Pro Very simple
It makes React look confusing as hell. Nothing against React - It's just that easy to implement!
Pro Scoped CSS available in components
Riot supports scoped CSS inside components for every browser by rewriting stylesheet rules.
Pro Lives well with any other library, framework and usage pattern
Since it's not opinionated, even the scripting can be in anything that can be transpired to JavaScript.
Pro Separation of concerns with RiotControl
RiotControl is inspired by Facebook's Flux Architecture Pattern and it's a simple Central Event Controller/Dispatcher for Riot. It's extremely lightweight (like Riot itself) but unfortunately passes up on some features in favor of performance and simplicity.
RiotControl helps with storing the stater of the application, by passing events from views to stores and vice-versa. Stores can communicate with many views and views can do the same with many stores, this enables to clearly separate concerns and inter-component communication.
Cons
Con Lack of typeclasses
Elm doesn't have typeclasses which means some code needs to be duplicated. A fix in a function that needs typeclasses means all of the duplicates need to be fixed too.
Con limited js interop
only one way ports are available as a crude js FFI. This means you can only call functions both directions but will not get a result.
Con Harder to get buy-in from devs and mgmt
It's a total divergence from what most people are used to in the JS ecosystem. The change in syntax can be scary, the change in approaching problems can be scary. The fact that it's not backed by FANG can be scary. The fact that it's not v1.0 can be scary. The governance model and the deliberately slow release cadence can be scary. There are a couple harsh medium articles, hackernews/reddit posts out there made by people with an ax to grind that can be scary if you don't have a better picture of the Elm community, the tradeoffs that have been made, or the benefits to be had over other options. None of these are good reasons to write off further investigation of a great tech, but it happens.
Con Code Repetition
Because of the lack of genericness Elm needs a lot of code to be repeated. There are 130+ implementations of map in elms core libraries.
Con Features get removed without warning
Often features that are deemed to be misused by the community like infix operators get removed without much of a warning.
Con Community harsh if criticised
If one even dares to start a discussion about a feature on elms slack, discord, subreddit or github one will be aggressively shut down often argueing that one should use purescript instead
Con Poor Windows support
Few if any of Elm's core contributors are Windows users and breaking bugs are sometimes left for weeks or months.
Con Good for beginners not good for experts
Development in elm is quite nice until you need some more advanced features. These however are actively discontinued and removed because elm wants to establish a "single way of doing things" philosophy
Con Updates break existing code often
The last few updates of elm broke existing code in major ways.
Con Adds an additional layer of abstraction
Some users claim that Elm adds an additional layer of abstraction, meaning that it is one more hurdle between the brain and the product.
Con Functional programming itself has quite a steep learning curve
Functional programming can be quite difficult to get your head around. It takes time to unlearn object orientational habits.
Con No Genericness in the future
Currently there is no code genericness like typeclasses possible, it has been officially stated that this will never change.
Con Not database-friendly
It is lots of work to make a server or database your "one source of truth", as Elm makes you write endless JSON parse boilerplate to talk to the server.
Con No Syntactic Sugar
Often you need to write longer and less readable code because there are no alternatives that are more concise.