Remove blank attributes from an Object in Javascript

var test = {
    test1 : null,
    test2 : 'somestring',
    test3 : 3,
}

for (i in test) {
  if (test[i] === null || test[i] === undefined) {
  // test[i] === undefined is probably not very useful here
    delete test[i];
  }
}

test.test1 === null; // true
test.test1 == null; // true

test.test4 === null; // false
test.test4 == null; // true

test.test4 === undefined; // true
test.test4 == undefined; // true

var obj = { };
obj.theProperty = 1;
delete obj.theProperty;

var test = {
   a: null,
   b: 'hello world',
   c: 12345
}

var newTest = $.grep(
                      test,
                      function(element, index) {
                         return (test[element] && test[element] != null);
                      }
                     );