How to delete an object of type Date in the Angular

How do I delete an object of type Date? I send to my component the object "obj" and I make a for to go through it

sendBtn(obj) {
    for (var propName in obj) {
        if (obj['untildate'] == "12/31/1969") {
            delete obj['untildate'];
          }
     }
}

This validation process works on all objects, but when I do this on this specific object "untildate", it returns me the value untildate=Invalid%20Date in the URL. Angular is not deleting it, and I wanted to find a way to get it