Variable inside setTimeout says it is undefined, but when outside it is defined

I have a class. I need to do some http work inside of a timeout. The problem I am faceing is the http variable inside the timeout keeps saying it is undefined.

export class MyClass {

    http:Http:

    constructor(private http:Http) {
        this.http = http;
    }

    sendFriendRequest(){

    this.http.post( ...//http variable is defined here
           setTimeout(function(){
               this.http.post(...  //http is not defined here
        }
   }
}