The never type in TypeScript is a fundamental concept that represents the type of values that will never occur. It is used in several specific scenarios to enhance type safety and error handling in TypeScript applications. Understanding the never type involves recognizing its purpose, how it differs from other types, and its common use cases.
Purpose of the never Type
The primary purpose of the never type is to represent values that should not exist or situations that should not happen within the code. It is a type that denotes the absence of every possible value. This might sound abstract at first, but it becomes clearer when you consider its applications in function return types, exhaustive checks, and advanced type manipulation.
How It Works
Function Return Type: When a function is expected not to return to its calling function because it throws an error or results in an infinite loop, its return type is annotated as never. This signals to the TypeScript compiler and to developers that no value will be returned from the function. For example, a function that throws an exception or enters an infinite loop can be typed as returning never[1][4].
Exhaustive Checks: In TypeScript, never is used in exhaustive type checks within switch-case statements or conditional blocks. If a variable is of a union type and all possible types are accounted for, TypeScript narrows down the type of the variable to never in the default case or after all cases are checked. This is useful for ensuring that all possible cases are handled[1].
Type Guards and Conditional Types: The never type is also utilized in advanced TypeScript patterns, such as type guards and conditional types, to exclude certain types from a union or to signal impossible code paths. For instance, using never in conditional types can help in filtering out types from a union, enhancing type safety a...
