Q:

Missing constructor body inside Class

I am reading type definition of react in here. Inside the code, I found inside class Component {} (in line 396), there is constructor without body as below (line 435 ):
constructor(props: Readonly<P>); 

Why there is no implementation of constructor inside a class. Can someone explain?

A:

you are reading index.d.ts 
its only typescript definition for javascript implementation. 
read more here

