code: function distinctUntilKeyChanged$2(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: /* tslint:disable:max-line-length 
  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