how can I declare a global variable in typescript

Inside a global.d.ts definition file

type MyProfileGlobal = (name: string,age:number) => void

Config.tsx file

In React:

interface Window {
  myProfileFun: MyProfileGlobal
}

In NodeJS:

declare module NodeJS {
  interface Global {
    myProfileFun: MyProfileGlobal
  }
}

Now you declare the root variable (that will actually live on window or global)

declare const myProfileFun: MyProfileGlobal;

Use it elsewhere in code, with either[Add data]:

global/* or window */.myProfileFun("Sagar",28);

myProfileFun("Sagar",28);

Use it elsewhere in code, with either[Get data]:

global/* or window */.myProfileFun= function (name: string,age:number) {
      console.log("Name: ", name);console.log("Age: ", name);
 };

The simplest way to declare a global variable in typescript:

// foo.ts
interface IData {
    test: string;
}
declare global {
    var someVar: IData;
}

Now, in any other file in the project:

// bar.ts
import 'foo'
somVar.test = 'Yes !!!!'