Union Types

When a value can be more than one type, use union types.

Union with or |

function logStatusCode(code: string | number) {
  // type | type
  console.log(`Status code: ${code}.`);
}
logStatusCode(404);
logStatusCode('404');

Union Type Errors

function logStatusCode2(code: string | number) {
  console.log(`Status code: ${code.toUpperCase()}.`);
  // error: Property 'toUpperCase' does not exist on type
  // 'string | number'.
}

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