How to extract a type from an array

type-extract-from-array.ts

// This is possible with Typescript 2.8+. You can declare an Unpacked<T> type as follows:

type Unpacked<T> = T extends (infer U)[] ? U : T;

type InnerCacheType = Unpacked<CacheType>; // Event | User
// This is a condensed definition of the Unpacked type given in the documentation.

// https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-8.html

type Unpacked<T> = T extends Array<infer U> ? U : T extends ReadonlyArray<infer U> ? U : T; 
// this works with ReadonlyArray as well –