Type 'BehaviorSubject<false>' is not assignable to type 'BehaviorSubject<boolean>'

Issue

I have this in one of my components:

public booleanSubject: BehaviorSubject<boolean> = new BehaviorSubject(false);

When I add "strictFunctionTypes": true to the tsconfig.json file I get the following error:

× Compiling TypeScript sources through NGC
ERROR: path/to/my/component.component.ts:28:10 - error TS2322: Type 'BehaviorSubject<false>' is not assignable to type 'BehaviorSubject<boolean>'.
  Types of property 'observers' are incompatible.
    Type 'Observer<false>[]' is not assignable to type 'Observer<boolean>[]'.
      Type 'Observer<false>' is not assignable to type 'Observer<boolean>'.
        Type 'boolean' is not assignable to type 'false'.

28   public booleanSubject: BehaviorSubject<boolean> = new BehaviorSubject(false);

Does anyone know the reason and how to get it not to throw the error by keeping the strictFunctionTypes flag set to true?

Solution

Igor Melo Telheiro answer is on point. Just to extend it a bit.

You can either declare that field with public booleanSubject = new BehaviorSubject(false); and it will automatically infer the right type BehaviorSubject<boolean>

Or you can declare the field with a type but then the assigned value must be also of that type when declared. public booleanSubject: BehaviorSubject<boolean> = new BehaviorSubject<boolean>(false);

Answered By - Panagiotis Bougioukos