A modern programming language that makes developers happier.

kotlinlang

what is the difference between the official multiplatform support and just manually compiling the same kotlin source once for the jdk and once for js?

“official multiplatform” also allows you to use actual/expect declarations

And also you can use `common` stdlib, so Idea and compiler will check that you use only APIs available for the all platforms

It is also possible to write tests in a common project so that they will be compiled and run in each platform project.