code: function distinctUntilKeyChanged(key, compare) {
  	    return distinctUntilChanged_1.distinctUntilChanged.call(this, function (x, y) {
  	        if (compare) {
  	            return compare(x[key], y[key]);
  	        }
  	        return x[key] === y[key];
  	    });
  	}
docs: Returns an Observable that emits all items emitted by the source Observable that are distinct by comparison from the previous item,
  using a property accessed by using the key provided to check if the two items are distinct.
  If a comparator function is provided, then it will be called for each item to test for whether or not that value should be emitted.
  If a comparator function is not provided, an equality check is used by default.
  @param {string} key string key for object property lookup on each item.
  @param {function} [compare] optional comparison function called to test if an item is distinct from the previous item in the source.
  @return {Observable} an Observable that emits items from the source Observable with distinct values based on the key specified.
  @method distinctUntilKeyChanged
  @owner Observable