ality test (watch out for coercions).
  return true if `a == b`
  # One is falsy and the other truthy.
  return false if (!a and b) or (a and !b)
  # One of them implements an `isEqual()`?
  return a.isEqual(b) if a.isEqual
  # Check dates' integer values.
  return a.getTime() is b.getTime() if _.isDate(a) and _.isDate(b)
  # Both are NaN?
  return false if _.isNaN(a) and _.isNaN(b)
  # Compare regular expressions.
  if _.isRegExp(a) and _.isRegExp(b)
    return a.source is b.source and
           a.global 