function _nextStep() {
    this._direction = 'forward';

    if (typeof (this._currentStepNumber) !== 'undefined') {
        for( var i = 0, len = this._introItems.length; i < len; i++ ) {
            var item = this._introItems[i];
            if( item.step === this._currentStepNumber ) {
                this._currentStep = i - 1;
                this._currentStepNumber = undefined;
            }
        }
    }

    if (typeof (this._currentStep) === 'undefined') {
      this._currentStep = 0;
    } else {
      ++this._currentStep;
    }

    if ((this._introItems.length) <= this._currentStep) {
      //end of the intro
      //check if any callback is defined
      if (typeof (this._introCompleteCallback) === 'function') {
        this._introCompleteCallback.call(this);
      }
      _exitIntro.call(this, this._targetElement);
      return;
    }

    var nextStep = this._introItems[this._currentStep];
    if (typeof (this._introBeforeChangeCallback) !== 'undefined') {
      this._introBeforeChangeCallback.call(this, nextStep.element);
    }

    _showElement.call(this, nextStep);
  }
Go to next step on intro

@api private
@method _nextStep