tests/cases/compiler/numberToString.ts(2,12): error TS2322: Type 'number' is not assignable to type 'string'. tests/cases/compiler/numberToString.ts(9,4): error TS2345: Argument of type 'number' is not assignable to parameter of type 'string'. ==== tests/cases/compiler/numberToString.ts (2 errors) ==== function f1(n:number):string { return n; // error return type mismatch ~ !!! error TS2322: Type 'number' is not assignable to type 'string'. } function f2(s:string):void { } f1(3); f2(3); // error no coercion to string ~ !!! error TS2345: Argument of type 'number' is not assignable to parameter of type 'string'. f2(3+""); // ok + operator promotes