function forIn(object, iteratee) {
      return object == null
        ? object
        : baseFor(object, getIteratee(iteratee, 3), keysIn);
    }
Iterates over own and inherited enumerable string keyed properties of an
object and invokes `iteratee` for each property. The iteratee is invoked
with three arguments: (value, key, object). Iteratee functions may exit
iteration early by explicitly returning `false`.

@static
@memberOf _
@since 0.3.0
@category Object
@param {Object} object The object to iterate over.
@param {Function} [iteratee=_.identity] The function invoked per iteration.
@returns {Object} Returns `object`.
@see _.forInRight
@example

function Foo() {
  this.a = 1;
  this.b = 2;
}

Foo.prototype.c = 3;

_.forIn(new Foo, function(value, key) {
  console.log(key);
});
// => Logs 'a', 'b', then 'c' (iteration order is not guaranteed).