Determine original name of variable after its passed to a function

You're right, this is very much impossible in any sane way, since only the value gets passed into the function.

This is now somehow possible thanks to ES6:

function getVariableName(unknownVariableInAHash){
  return Object.keys(unknownVariableInAHash)[0]
}

const foo = 42
const bar = 'baz'
console.log(getVariableName({foo})) //returns string "foo"
console.log(getVariableName({bar})) //returns string "bar"

The only (small) catch is that you have to wrap your unknown variable between {}, which is no big deal.

Well, all the global variables are properties of global object (this or window), aren't they? So when I wanted to find out the name of my variables, I made following function:

var getName = function(variable) {
  for (var prop in window) {
    if (variable === window[prop]) {
      return prop;
    }
  }
}
var helloWorld = "Hello World!";
console.log(getName(helloWorld)); // "helloWorld"

Sometimes doesn't work, for example, if 2 strings are created without new operator and have the same value.

As you want debugging (show name of var and value of var), I've been looking for it too, and just want to share my finding.

It is not by retrieving the name of the var from the var but the other way around : retrieve the value of the var from the name (as string) of the var.

It is possible to do it without eval, and with very simple code, at the condition you pass your var into the function with quotes around it, and you declare the variable globally :

foo = 'bar';

debug('foo'); 

function debug(Variable) { 
 var Value = this[Variable]; // in that occurrence, it is equivalent to
 // this['foo'] which is the syntax to call the global variable foo
 console.log(Variable + " is " + Value);  // print "foo is bar"
}