TS2345: Argument of type 'X' is not assignable to parameter of type 'Y'

Workarounds

1. 90% success Transform the argument to match the expected type before passing

   // Convert string to number:
   parseInt(value, 10)
   // Convert to expected shape:
   const arg: ExpectedType = {
     ...input,
     missingField: defaultValue
   };
   fn(arg);

   Sources: https://www.typescriptlang.org/docs/handbook/2/narrowing.html

2. 85% success Use function overloads or generics to accept multiple types safely

   Use function overloads or generics to accept multiple types safely

   Sources: https://www.typescriptlang.org/docs/handbook/2/generics.html

3. 87% success Create a type guard to narrow the type before the function call

   function isString(value: unknown): value is string {
     return typeof value === 'string';
   }
   
   const input: string | number = getValue();
   if (isString(input)) {
     // input is narrowed to string here
     processString(input);
   }

   Sources: https://www.typescriptlang.org/docs/handbook/2/narrowing.html#using-type-predicates