How to choose between never , unknown , and any in TypeScript?

Choosing between never, unknown, and any in TypeScript depends on the specific requirements of your code and the level of type safety you wish to enforce. Each of these types serves a different purpose and has its own use cases.

any

• Usage: The any type is the most permissive type in TypeScript. It is essentially a way to opt-out of the type-checking system. When a variable is declared with the any type, you can assign it any value, and TypeScript will not perform any checking on operations involving this type.
• When to Use:
  • You should use any when you are migrating a JavaScript project to TypeScript and you initially do not know the types of some variables.
  • It is also useful when dealing with dynamic content whose type is not known until runtime.
  • However, overuse of any can lead to code that loses the benefits of TypeScript's type system, potentially leading to runtime errors that the compiler cannot detect[1][3][5].

unknown

• Usage: The unknown type represents any value but is safer than any because you cannot perform any operations on an unknown value without first asserting or narrowing the type to a more specific type.
• When to Use:
  • Use unknown when you want to ensure that the type of variables is checked at some point in your code, but you do not initially know the type.
  • It is ideal for functions that return a value fetched from an API or user input, where you need to validate the type before proceeding[1][2][3][4].

never

• Usage: The never type represents values that never occur. For example, a function that throws an exception or one that runs an infinite loop without returning does not return a value to the calling function, thus having a return type of never.
• When to Use:
  • Use never for functions that are not expected to return a value ever, such as those that always throw an error or terminate the application.
  • It is also used in exhaustive checks, where you want to ensure that a switch statement or similar construct has handled all possible cases[1][3][5].

Practical Examples and Considerations

• Type Safety: unknown is safer than any because it forces you to perform type checking before performing operations on values, thus catching potential bu...