Type 'null' is not assignable to type 'T'

Question

I have this generic method

class Foo {       public static bar<T>(x: T): T {          ...          if(x === null)              return null; //<------- syntax error          ...      }  }   ... //somewhere const x = Foo.bar<number | null>(1); 

I'm getting the syntax error

TS2322: Type 'null' is not assignable to type 'T'.

I'm expecting this to compile because T could be null.

what is the proper way to solve this problem

Answer 1

You have to declare the return type as null or turn off strictNullChecks in your tsconfig

public static bar<T>(x: T): T | null 

or you could type null as any e.g.

 return null as any; 

Answer 2

Since version 3.9.5, TypeScript enforces strictNullChecks on numbers and strings just to name a few. For example, the following code will throw an error during compilation:

let x: number = null; 

To avoid this error you have two options:

• Set strictNullChecks=false in tsconfig.json.
• Declare your variable type as any:

  let x: any = null;