deepComparison.js

/*
The == operator compares objects by identity. But sometimes, you would prefer
to compare the values of their actual properties. Write a function, deepEqual,
that takes two values and returns true only if they are the same value or are
objects with the same properties whose values are also equal when compared with
a recursive call to deepEqual . To find out whether to compare two things by
identity (use the === operator for that) or by looking at their properties, you
can use the typeof operator. If it produces "object" for both values, you
should do a deep comparison. But you have to take one silly exception into
account: by a historical accident, typeof null also produces "object" .
*/
function deepEqual(a, b) {
  if (a === b) return true;

  if (a == null || typeof a != "object" ||
      b == null || typeof b != "object")
    return false;

  var propsInA = 0, propsInB = 0;

  for (var prop in a)
    propsInA += 1;

  for (var prop in b) {
    propsInB += 1;
    if (!(prop in a) || !deepEqual(a[prop], b[prop]))
      return false;
  }

  return propsInA == propsInB;
}