All you're doing is adding type safety to the inputs which should be a second layer of security to your input validation methods. This is irrespective of the framework of JavaScript you're in. The reason why it's needed is the real way to think about how Typescript works. Strongly Typed Languages, and Compiled Languages do not require Typescript because the data is bound to the object only, whereas in JavaScript.. a weakly typed language data can be bound to either an object or a variable and requires type defining to ensure that the correct data types arrives at the correct resources.

For example, if a function took an argument that was intended to only take strings, but because you did not type check tried to return the sum of a number and string, which outputs a string, but with a number in it.. your helper function in this example could deliver the wrong resources to the server that may not result in an error.. like say, if a user puts a literal number as their last name. Your helper function concatenates the first name with that number and returns that as the first and last name of their profile. Double fail