Typescript generics

genericsExample.ts

function map<A, B>(arr: A[], fn: (el: A) => B): B[] {
  return arr.map(fn);
}

// manual annotation
map<number, void>(['string'], el => el * 2)

// inferred annotation 
map([1,2,4], (num) => num * 2)


function mapNumberArray(arr: number[], fn: (el: number) => number[]) {
  return arr.map(fn);
}