This is likely referring to TypeScript.

TypeScript has all of these patterns, they are used very frequently and they are necessary because TypeScript tends to be interesting from time to time since its types only exist at compile time, because it compiles to JavaScript, which is a language without types.

TypeScript also allows any as a keyword, which says "I don't know which type this is and I don't care", which still produces valid JavaScript. To get back to typed variables it is necessary to use typeof (or similar constructs like a type guard).

https://www.typescriptlang.org/docs/handbook/2/typeof-types.html