Generic

// generics - like Java

function identity<T>(arg: T): T {

// explicit and (more common) implicit way of using it

let output = identity<string>("myString"); 

let output = identity("myString"); 

// generic constraints

function loggingIdentity<T extends Lengthwise>(arg:T):T{

   // something here

}

function getProperty<T, K extends keyof T>(obj: T, key: K) {

  return obj[key];

}

declare function create<T extends HTMLElement = HTMLDivElement, U = T[]>(

  element?: T,

  children?: U

): Container<T, U>;