How to tell which key called a function in javascript

Question

If I have an object with multiple keys calling the same function and this function is implemented outside its scope, how to determine which key called this function? For example:

function tellYourAge() {
   return function()
   {
       // I already know here that this refers to Population
       // For example, console.log(this) will print the Population object
   }
}

{
   let Population = {
     Mahdi: tellYourAge(),
     Samuel: tellYourAge(),
     Jon: tellYourAge()
   };

   Population.Mahdi(); // It should log 18
   Population.Samuel(); // It should log 20
   Population.Jon(); // It should log 21
}

Answer 1

It is possible

function tellYourAge() {
   return function()
   {
       var f = arguments.callee;
       var key = Object.keys(this).filter(key => this[key] === f)[0];
       console.log(key);
   }
}

{
   let Population = {
     Mahdi: tellYourAge(),
     Samuel: tellYourAge(),
     Jon: tellYourAge()
   };

   Population.Mahdi(); // prints Mahdi
   Population.Samuel(); // prints Samuel
   Population.Jon(); // prints Jon
}

Explanation: arguments.callee is reference to the function to which the arguments object belongs. And this is basically "a thing before the dot" at the moment of function invocation, therefore your Population object. Now what you do is lookup the called function instance in the object and you are done.