How to cast inside .tsx file?

I wrote some code inside a .tsx file and I need to cast a variable but it doesn't work and I don't understand why.

That is my code :

let a : number = 2;let b : string = a as unknown as string;console.log("b type = "+typeof(b))

And that is the result :

b type = number

I think this is because I cast as unknown and then as string and I don't know why it's necessary but if I just write : let b : string = a as string;, I get the following error :

ERROR in App.tsx(59,22)  TS2352: Conversion of type 'number' to type 'string' may be a mistake because neither type sufficiently overlaps with the other. If this was intentional, convert the expression to 'unknown' first.

So does anyone know how to cast in .tsx file ? ( It's not possible to use <> for type casting otherwise it's considered as a React Element)