Elm

Elm uses type inference to detect corner cases and give friendly hints. NoRedInk switched to Elm about four years ago, and 300k+ lines later, they still have not had to scramble to fix a confusing runtime exception in production. The compiler guides you safely through your changes, ensuring confidence even through the most wide-reaching refactorings in unfamiliar codebases. Including your own, six months later. All Elm programs are written in the same pattern, eliminating doubt and lengthy discussions when deciding how to build new projects and making it easy to navigate old or foreign codebases. Enjoy Elm's famously helpful error messages. Even on codebases with hundreds of thousands of lines of code, the compilation is done in a blink. Elm has its own virtual DOM implementation, designed for simplicity and speed. All values are immutable in Elm, and the benchmarks show that this helps us generate particularly fast JavaScript code.