> that's about a certain IDE not the language itself This stuff is only possible if you can analyze the code statically. With JS, which is running in a browse

> that's about a certain IDE not the language itself This stuff is only possible if you can analyze the code statically. With JS, which is running in a browser, you don't know anything. You don't know what other kinds of scripts are running on that page. You don't know which globals these introduce or which built-ins they modify. E.g.: Math.round(5).length You don't know if Number has a length property. You don't know if "round" takes a Number as argument. You don't know what this "round" function returns. You don't know if the "round" function exists. You don't know if a "Math" global exists. For tools, this is a big problem. In Dart, the analyzer knows about all these things. If the function is annotated, I'll get all the tooling and checks. > Care to back that up? No. You can't even imagine what good tooling is like. Naturally, you're blind to the friction which is caused by a lack of good tooling.