TypeScript docs say nothing about loop like for or for-in. From playing with the language it seems that only any or string variables are supported in for loop.
Why has this decision been made?
Why not use the type information and have strongly-typed iteration variable?
The for-in statement is really there to enumerate over object properties, which is how it is implemented in TypeScript. There are some issues with using it on arrays.
I can’t speak on behalf of the TypeScript team, but I believe this is the reason for the implementation in the language.