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Learning TypeScript 2.x - Second Edition
book

Learning TypeScript 2.x - Second Edition

by Remo H. Jansen
April 2018
Beginner content levelBeginner
536 pages
13h 21m
English
Packt Publishing
Content preview from Learning TypeScript 2.x - Second Edition

The never type

As described in the TypeScript documentation, the never type has the following characteristics:

  • The never type is a subtype of and assignable to every type.
  • No type is a subtype of or assignable to never (except never itself).
  • In a function expression or arrow function with no return type annotation, if the function has no return statements or only return statements with expressions of type never and, if the end point of the function is not reachable (as determined by control flow analysis), the inferred return type for the function is never.
  • In a function with an explicit never return type annotation, all return statements (if any) must have expressions of a type never and the end of the function must not be reachable.
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Publisher Resources

ISBN: 9781788391474Supplemental Content