complete = function complete() {
          if (_this.config.animation) {
            _this._fixTransition();
          }

          var prevHoverState = _this._hoverState;
          _this._hoverState = null;
          $(_this.element).trigger(_this.constructor.Event.SHOWN);

          if (prevHoverState === HoverState.OUT) {
            _this._leave(null, _this);
          }
        }
Check for Popper dependency
Popper - https://popper.js.org