type alphanumeric = string | number; let input: alphanumeric; input = 100; // valid input = 'Hi'; // valid input = false; // Compiler error Code language: JavaScript (javascript)type StringAlias = string; type NumberAlias = number; // aliases for 'normal' types type SixAlias = 6; type MyFavouriteFood = "burger"; // aliases for 'literal' types // these are usually useless on their own type Food = MyFavouriteFood | "pizza" | "pasta" | "salad"; // they get useful when you combine them: // a Food can be one of these choices. type Foods = Food[]; // this is an alias for an array of Foods. type SuccessfulResponse = { message: string, statusCode: number, attachment?: string, preferredFoods?: Foods, } // Now we define a SuccessfulResponse type as the type of a // JS literal object with two required and two optional attributes. // Note that you could also use an interface in this case. type SuccessfulResponseHandler = (res: SuccessfulResponse) => void; // This is a type alias for a function. // tl;dr: You can alias every type in TypeScript and chain them. // This is very useful for reusability and readability.check the file extention and change it to .ts/tsx format