String Literal and Overload Function

A parameter with a string literal

A function can use a string literal as its parameter to know which return type is possible. For example, it’s possible to have a function with a string parameter and have many overloads where a specific string value will cause the execution of one function or another.

In the example below, the method accepts only the strings, "batman" and "superman", even if the signature shows a string. See lines 12 and 13. TypeScript unites both overloads to create a string literal of all the overloads.

For example, if you are using an IDE that supports TypeScript, the IDE will show the return type, Batman if the parameter is "batman". Line 14 combines all the overload.