intro.js

/**
 * Intro.js v0.8.0
 * https://github.com/usablica/intro.js
 * MIT licensed
 *
 * Copyright (C) 2013 usabli.ca - A weekend project by Afshin Mehrabani (@afshinmeh)
 */

(function (root, factory) {
  if (typeof exports === 'object') {
    // CommonJS
    factory(exports);
  } else if (typeof define === 'function' && define.amd) {
    // AMD. Register as an anonymous module.
    define(['exports'], factory);
  } else {
    // Browser globals
    factory(root);
  }
} (this, function (exports) {
  //Default config/variables
  var VERSION = '0.8.0';

  /**
   * IntroJs main class
   *
   * @class IntroJs
   */
  function IntroJs(obj) {
    this._targetElement = obj;

    this._options = {
      /* Next button label in tooltip box */
      nextLabel: 'Next &rarr;',
      /* Previous button label in tooltip box */
      prevLabel: '&larr; Back',
      /* Skip button label in tooltip box */
      skipLabel: 'Skip',
      /* Done button label in tooltip box */
      doneLabel: 'Done',
      /* Default tooltip box position */
      tooltipPosition: 'bottom',
      /* Next CSS class for tooltip boxes */
      tooltipClass: '',
      /* Close introduction when pressing Escape button? */
      exitOnEsc: true,
      /* Close introduction when clicking on overlay layer? */
      exitOnOverlayClick: true,
      /* Show step numbers in introduction? */
      showStepNumbers: true,
      /* Let user use keyboard to navigate the tour? */
      keyboardNavigation: true,
      /* Show tour control buttons? */
      showButtons: true,
      /* Show tour bullets? */
      showBullets: true,
      /* Scroll to highlighted element? */
      scrollToElement: true
    };
  }

  /**
   * Initiate a new introduction/guide from an element in the page
   *
   * @api private
   * @method _introForElement
   * @param {Object} targetElm
   * @returns {Boolean} Success or not?
   */
  function _introForElement(targetElm) {
    var introItems = [],
        self = this;

    if (this._options.steps) {
      //use steps passed programmatically
      var allIntroSteps = [];

      for (var i = 0, stepsLength = this._options.steps.length; i < stepsLength; i++) {
        var currentItem = _cloneObject(this._options.steps[i]);
        //set the step
        currentItem.step = introItems.length + 1;
        //use querySelector function only when developer used CSS selector
        if (typeof(currentItem.element) === 'string') {
          //grab the element with given selector from the page
          currentItem.element = document.querySelector(currentItem.element);
        }

        //intro without element
        if (typeof(currentItem.element) === 'undefined' || currentItem.element == null) {
          var floatingElementQuery = document.querySelector(".introjsFloatingElement");

          if (floatingElementQuery == null) {
            floatingElementQuery = document.createElement('div');
            floatingElementQuery.className = 'introjsFloatingElement';

            document.body.appendChild(floatingElementQuery);
          }

          currentItem.element  = floatingElementQuery;
          currentItem.position = 'floating';
        }

        if (currentItem.element != null) {
          introItems.push(currentItem);
        }
      }

    } else {
       //use steps from data-* annotations
      var allIntroSteps = targetElm.querySelectorAll('*[data-intro]');
      //if there's no element to intro
      if (allIntroSteps.length < 1) {
        return false;
      }

      //first add intro items with data-step
      for (var i = 0, elmsLength = allIntroSteps.length; i < elmsLength; i++) {
        var currentElement = allIntroSteps[i];
        var step = parseInt(currentElement.getAttribute('data-step'), 10);

        if (step > 0) {
          introItems[step - 1] = {
            element: currentElement,
            intro: currentElement.getAttribute('data-intro'),
            step: parseInt(currentElement.getAttribute('data-step'), 10),
            tooltipClass: currentElement.getAttribute('data-tooltipClass'),
            position: currentElement.getAttribute('data-position') || this._options.tooltipPosition
          };
        }
      }

      //next add intro items without data-step
      //todo: we need a cleanup here, two loops are redundant
      var nextStep = 0;
      for (var i = 0, elmsLength = allIntroSteps.length; i < elmsLength; i++) {
        var currentElement = allIntroSteps[i];

        if (currentElement.getAttribute('data-step') == null) {

          while (true) {
            if (typeof introItems[nextStep] == 'undefined') {
              break;
            } else {
              nextStep++;
            }
          }

          introItems[nextStep] = {
            element: currentElement,
            intro: currentElement.getAttribute('data-intro'),
            step: nextStep + 1,
            tooltipClass: currentElement.getAttribute('data-tooltipClass'),
            position: currentElement.getAttribute('data-position') || this._options.tooltipPosition
          };
        }
      }
    }

    //removing undefined/null elements
    var tempIntroItems = [];
    for (var z = 0; z < introItems.length; z++) {
      introItems[z] && tempIntroItems.push(introItems[z]);  // copy non-empty values to the end of the array
    }

    introItems = tempIntroItems;

    //Ok, sort all items with given steps
    introItems.sort(function (a, b) {
      return a.step - b.step;
    });

    //set it to the introJs object
    self._introItems = introItems;

    //add overlay layer to the page
    if(_addOverlayLayer.call(self, targetElm)) {
      //then, start the show
      _nextStep.call(self);

      var skipButton     = targetElm.querySelector('.introjs-skipbutton'),
          nextStepButton = targetElm.querySelector('.introjs-nextbutton');

      self._onKeyDown = function(e) {
        if (e.keyCode === 27 && self._options.exitOnEsc == true) {
          //escape key pressed, exit the intro
          _exitIntro.call(self, targetElm);
          //check if any callback is defined
          if (self._introExitCallback != undefined) {
            self._introExitCallback.call(self);
          }
        } else if(e.keyCode === 37) {
          //left arrow
          _previousStep.call(self);
        } else if (e.keyCode === 39 || e.keyCode === 13) {
          //right arrow or enter
          _nextStep.call(self);
          //prevent default behaviour on hitting Enter, to prevent steps being skipped in some browsers
          if(e.preventDefault) {
            e.preventDefault();
          } else {
            e.returnValue = false;
          }
        }
      };

      self._onResize = function(e) {
        _setHelperLayerPosition.call(self, document.querySelector('.introjs-helperLayer'));
      };

      if (window.addEventListener) {
        if (this._options.keyboardNavigation) {
          window.addEventListener('keydown', self._onKeyDown, true);
        }
        //for window resize
        window.addEventListener("resize", self._onResize, true);
      } else if (document.attachEvent) { //IE
        if (this._options.keyboardNavigation) {
          document.attachEvent('onkeydown', self._onKeyDown);
        }
        //for window resize
        document.attachEvent("onresize", self._onResize);
      }
    }
    return false;
  }

 /*
   * makes a copy of the object
   * @api private
   * @method _cloneObject
  */
  function _cloneObject(object) {
      if (object == null || typeof (object) != 'object' || typeof (object.nodeType) != 'undefined') {
          return object;
      }
      var temp = {};
      for (var key in object) {
          temp[key] = _cloneObject(object[key]);
      }
      return temp;
  }
  /**
   * Go to specific step of introduction
   *
   * @api private
   * @method _goToStep
   */
  function _goToStep(step) {
    //because steps starts with zero
    this._currentStep = step - 2;
    if (typeof (this._introItems) !== 'undefined') {
      _nextStep.call(this);
    }
  }

  /**
   * Go to next step on intro
   *
   * @api private
   * @method _nextStep
   */
  function _nextStep() {
    this._direction = 'forward';

    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 previous step on intro
   *
   * @api private
   * @method _nextStep
   */
  function _previousStep() {
    this._direction = 'backward';
    
    if (this._currentStep === 0) {
      return false;
    }

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

    _showElement.call(this, nextStep);
  }

  /**
   * Exit from intro
   *
   * @api private
   * @method _exitIntro
   * @param {Object} targetElement
   */
  function _exitIntro(targetElement) {
    //remove overlay layer from the page
    var overlayLayer = targetElement.querySelector('.introjs-overlay');
    
    //return if intro already completed or skipped
    if (overlayLayer == null) {
      return;
    }

    //for fade-out animation
    overlayLayer.style.opacity = 0;
    setTimeout(function () {
      if (overlayLayer.parentNode) {
        overlayLayer.parentNode.removeChild(overlayLayer);
      }
    }, 500);

    //remove all helper layers
    var helperLayer = targetElement.querySelector('.introjs-helperLayer');
    if (helperLayer) {
      helperLayer.parentNode.removeChild(helperLayer);
    }

    //remove intro floating element
    var floatingElement = document.querySelector('.introjsFloatingElement');
    if (floatingElement) {
      floatingElement.parentNode.removeChild(floatingElement);
    }

    //remove `introjs-showElement` class from the element
    var showElement = document.querySelector('.introjs-showElement');
    if (showElement) {
      showElement.className = showElement.className.replace(/introjs-[a-zA-Z]+/g, '').replace(/^\s+|\s+$/g, ''); // This is a manual trim.
    }

    //remove `introjs-fixParent` class from the elements
    var fixParents = document.querySelectorAll('.introjs-fixParent');
    if (fixParents && fixParents.length > 0) {
      for (var i = fixParents.length - 1; i >= 0; i--) {
        fixParents[i].className = fixParents[i].className.replace(/introjs-fixParent/g, '').replace(/^\s+|\s+$/g, '');
      };
    }

    //clean listeners
    if (window.removeEventListener) {
      window.removeEventListener('keydown', this._onKeyDown, true);
    } else if (document.detachEvent) { //IE
      document.detachEvent('onkeydown', this._onKeyDown);
    }
    
    //set the step to zero
    this._currentStep = undefined;
  }

  /**
   * Render tooltip box in the page
   *
   * @api private
   * @method _placeTooltip
   * @param {Object} targetElement
   * @param {Object} tooltipLayer
   * @param {Object} arrowLayer
   */
  function _placeTooltip(targetElement, tooltipLayer, arrowLayer, helperNumberLayer) {
    //reset the old style
    tooltipLayer.style.top        = null;
    tooltipLayer.style.right      = null;
    tooltipLayer.style.bottom     = null;
    tooltipLayer.style.left       = null;
    tooltipLayer.style.marginLeft = null;
    tooltipLayer.style.marginTop  = null;

    arrowLayer.style.display = 'inherit';

    if (typeof(helperNumberLayer) != 'undefined' && helperNumberLayer != null) {
      helperNumberLayer.style.top  = null;
      helperNumberLayer.style.left = null;
    }

    //prevent error when `this._currentStep` is undefined
    if (!this._introItems[this._currentStep]) return;

    var tooltipCssClass = '';

    //if we have a custom css class for each step
    var currentStepObj = this._introItems[this._currentStep];
    if (typeof (currentStepObj.tooltipClass) === 'string') {
      tooltipCssClass = currentStepObj.tooltipClass;
    } else {
      tooltipCssClass = this._options.tooltipClass;
    }

    tooltipLayer.className = ('introjs-tooltip ' + tooltipCssClass).replace(/^\s+|\s+$/g, '');

    //custom css class for tooltip boxes
    var tooltipCssClass = this._options.tooltipClass;

    var currentTooltipPosition = this._introItems[this._currentStep].position;
    switch (currentTooltipPosition) {
      case 'top':
        tooltipLayer.style.left = '15px';
        tooltipLayer.style.top = '-' + (_getOffset(tooltipLayer).height + 10) + 'px';
        arrowLayer.className = 'introjs-arrow bottom';
        break;
      case 'right':
        tooltipLayer.style.left = (_getOffset(targetElement).width + 20) + 'px';
        arrowLayer.className = 'introjs-arrow left';
        break;
      case 'left':
        if (this._options.showStepNumbers == true) {  
          tooltipLayer.style.top = '15px';
        }
        tooltipLayer.style.right = (_getOffset(targetElement).width + 20) + 'px';
        arrowLayer.className = 'introjs-arrow right';
        break;
      case 'floating':
        arrowLayer.style.display = 'none';

        //we have to adjust the top and left of layer manually for intro items without element{
        var tooltipOffset = _getOffset(tooltipLayer);

        tooltipLayer.style.left   = '50%';
        tooltipLayer.style.top    = '50%';
        tooltipLayer.style.marginLeft = '-' + (tooltipOffset.width / 2)  + 'px';
        tooltipLayer.style.marginTop  = '-' + (tooltipOffset.height / 2) + 'px';

        if (typeof(helperNumberLayer) != 'undefined' && helperNumberLayer != null) {
          helperNumberLayer.style.left = '-' + ((tooltipOffset.width / 2) + 18) + 'px';
          helperNumberLayer.style.top  = '-' + ((tooltipOffset.height / 2) + 18) + 'px';
        }

        break;
      case 'bottom':
      // Bottom going to follow the default behavior
      default:
        tooltipLayer.style.bottom = '-' + (_getOffset(tooltipLayer).height + 10) + 'px';
        arrowLayer.className = 'introjs-arrow top';
        break;
    }
  }

  /**
   * Update the position of the helper layer on the screen
   *
   * @api private
   * @method _setHelperLayerPosition
   * @param {Object} helperLayer
   */
  function _setHelperLayerPosition(helperLayer) {
    if (helperLayer) {
      //prevent error when `this._currentStep` in undefined
      if (!this._introItems[this._currentStep]) return;

      var currentElement  = this._introItems[this._currentStep];
      var elementPosition = _getOffset(currentElement.element);

      var widthHeightPadding = 10;
      if (currentElement.position == 'floating') {
        widthHeightPadding = 0;
      }

      //set new position to helper layer
      helperLayer.setAttribute('style', 'width: ' + (elementPosition.width  + widthHeightPadding)  + 'px; ' +
                                        'height:' + (elementPosition.height + widthHeightPadding)  + 'px; ' +
                                        'top:'    + (elementPosition.top    - 5)   + 'px;' +
                                        'left: '  + (elementPosition.left   - 5)   + 'px;');
    }
  }

  /**
   * Show an element on the page
   *
   * @api private
   * @method _showElement
   * @param {Object} targetElement
   */
  function _showElement(targetElement) {

    if (typeof (this._introChangeCallback) !== 'undefined') {
        this._introChangeCallback.call(this, targetElement.element);
    }

    var self = this,
        oldHelperLayer = document.querySelector('.introjs-helperLayer'),
        elementPosition = _getOffset(targetElement.element);

    if (oldHelperLayer != null) {
      var oldHelperNumberLayer = oldHelperLayer.querySelector('.introjs-helperNumberLayer'),
          oldtooltipLayer      = oldHelperLayer.querySelector('.introjs-tooltiptext'),
          oldArrowLayer        = oldHelperLayer.querySelector('.introjs-arrow'),
          oldtooltipContainer  = oldHelperLayer.querySelector('.introjs-tooltip'),
          skipTooltipButton    = oldHelperLayer.querySelector('.introjs-skipbutton'),
          prevTooltipButton    = oldHelperLayer.querySelector('.introjs-prevbutton'),
          nextTooltipButton    = oldHelperLayer.querySelector('.introjs-nextbutton');

      //hide the tooltip
      oldtooltipContainer.style.opacity = 0;

      if (oldHelperNumberLayer != null) {
        var lastIntroItem = this._introItems[(targetElement.step - 2 >= 0 ? targetElement.step - 2 : 0)];

        if (lastIntroItem != null && (this._direction == 'forward' && lastIntroItem.position == 'floating') || (this._direction == 'backward' && targetElement.position == 'floating')) {
          oldHelperNumberLayer.style.opacity = 0;
        }
      }

      //set new position to helper layer
      _setHelperLayerPosition.call(self, oldHelperLayer);

      //remove `introjs-fixParent` class from the elements
      var fixParents = document.querySelectorAll('.introjs-fixParent');
      if (fixParents && fixParents.length > 0) {
        for (var i = fixParents.length - 1; i >= 0; i--) {
          fixParents[i].className = fixParents[i].className.replace(/introjs-fixParent/g, '').replace(/^\s+|\s+$/g, '');
        };
      }

      //remove old classes
      var oldShowElement = document.querySelector('.introjs-showElement');
      oldShowElement.className = oldShowElement.className.replace(/introjs-[a-zA-Z]+/g, '').replace(/^\s+|\s+$/g, '');
      //we should wait until the CSS3 transition is competed (it's 0.3 sec) to prevent incorrect `height` and `width` calculation
      if (self._lastShowElementTimer) {
        clearTimeout(self._lastShowElementTimer);
      }
      self._lastShowElementTimer = setTimeout(function() {
        //set current step to the label
        if (oldHelperNumberLayer != null) {
          oldHelperNumberLayer.innerHTML = targetElement.step;
        }
        //set current tooltip text
        oldtooltipLayer.innerHTML = targetElement.intro;
        //set the tooltip position
        _placeTooltip.call(self, targetElement.element, oldtooltipContainer, oldArrowLayer, oldHelperNumberLayer);

        //change active bullet
        oldHelperLayer.querySelector('.introjs-bullets li > a.active').className = '';
        oldHelperLayer.querySelector('.introjs-bullets li > a[data-stepnumber="' + targetElement.step + '"]').className = 'active';

        //show the tooltip
        oldtooltipContainer.style.opacity = 1;
        oldHelperNumberLayer.style.opacity = 1;
      }, 350);

    } else {
      var helperLayer       = document.createElement('div'),
          arrowLayer        = document.createElement('div'),
          tooltipLayer      = document.createElement('div'),
          tooltipTextLayer  = document.createElement('div'),
          bulletsLayer      = document.createElement('div'),
          buttonsLayer      = document.createElement('div');

      helperLayer.className = 'introjs-helperLayer';

      //set new position to helper layer
      _setHelperLayerPosition.call(self, helperLayer);

      //add helper layer to target element
      this._targetElement.appendChild(helperLayer);

      arrowLayer.className = 'introjs-arrow';

      tooltipTextLayer.className = 'introjs-tooltiptext';
      tooltipTextLayer.innerHTML = targetElement.intro;

      bulletsLayer.className = 'introjs-bullets';

      if (this._options.showBullets === false) {
        bulletsLayer.style.display = 'none';
      }

      var ulContainer = document.createElement('ul');

      for (var i = 0, stepsLength = this._introItems.length; i < stepsLength; i++) {
        var innerLi    = document.createElement('li');
        var anchorLink = document.createElement('a');

        anchorLink.onclick = function() {
          self.goToStep(this.getAttribute('data-stepnumber'));
        };

        if (i === 0) anchorLink.className = "active";

        anchorLink.href = 'javascript:void(0);';
        anchorLink.innerHTML = "&nbsp;";
        anchorLink.setAttribute('data-stepnumber', this._introItems[i].step);

        innerLi.appendChild(anchorLink);
        ulContainer.appendChild(innerLi);
      }

      bulletsLayer.appendChild(ulContainer);

      buttonsLayer.className = 'introjs-tooltipbuttons';
      if (this._options.showButtons === false) {
        buttonsLayer.style.display = 'none';
      }

      tooltipLayer.className = 'introjs-tooltip';
      tooltipLayer.appendChild(tooltipTextLayer);
      tooltipLayer.appendChild(bulletsLayer);

      //add helper layer number
      if (this._options.showStepNumbers == true) {
        var helperNumberLayer = document.createElement('span');
        helperNumberLayer.className = 'introjs-helperNumberLayer';
        helperNumberLayer.innerHTML = targetElement.step;
        helperLayer.appendChild(helperNumberLayer);
      }
      tooltipLayer.appendChild(arrowLayer);
      helperLayer.appendChild(tooltipLayer);

      //next button
      var nextTooltipButton = document.createElement('a');

      nextTooltipButton.onclick = function() {
        if (self._introItems.length - 1 != self._currentStep) {
          _nextStep.call(self);
        }
      };

      nextTooltipButton.href = 'javascript:void(0);';
      nextTooltipButton.innerHTML = this._options.nextLabel;

      //previous button
      var prevTooltipButton = document.createElement('a');

      prevTooltipButton.onclick = function() {
        if (self._currentStep != 0) {
          _previousStep.call(self);
        }
      };

      prevTooltipButton.href = 'javascript:void(0);';
      prevTooltipButton.innerHTML = this._options.prevLabel;

      //skip button
      var skipTooltipButton = document.createElement('a');
      skipTooltipButton.className = 'introjs-button introjs-skipbutton';
      skipTooltipButton.href = 'javascript:void(0);';
      skipTooltipButton.innerHTML = this._options.skipLabel;

      skipTooltipButton.onclick = function() {
        if (self._introItems.length - 1 == self._currentStep && typeof (self._introCompleteCallback) === 'function') {
          self._introCompleteCallback.call(self);
        }

        if (self._introItems.length - 1 != self._currentStep && typeof (self._introExitCallback) === 'function') {
          self._introExitCallback.call(self);
        }

        _exitIntro.call(self, self._targetElement);
      };

      buttonsLayer.appendChild(skipTooltipButton);

      //in order to prevent displaying next/previous button always
      if (this._introItems.length > 1) {
        buttonsLayer.appendChild(prevTooltipButton);
        buttonsLayer.appendChild(nextTooltipButton);
      }

      tooltipLayer.appendChild(buttonsLayer);

      //set proper position
      _placeTooltip.call(self, targetElement.element, tooltipLayer, arrowLayer, helperNumberLayer);
    }

    if (this._currentStep == 0 && this._introItems.length > 1) {
      prevTooltipButton.className = 'introjs-button introjs-prevbutton introjs-disabled';
      nextTooltipButton.className = 'introjs-button introjs-nextbutton';
      skipTooltipButton.innerHTML = this._options.skipLabel;
    } else if (this._introItems.length - 1 == this._currentStep || this._introItems.length == 1) {
      skipTooltipButton.innerHTML = this._options.doneLabel;
      prevTooltipButton.className = 'introjs-button introjs-prevbutton';
      nextTooltipButton.className = 'introjs-button introjs-nextbutton introjs-disabled';
    } else {
      prevTooltipButton.className = 'introjs-button introjs-prevbutton';
      nextTooltipButton.className = 'introjs-button introjs-nextbutton';
      skipTooltipButton.innerHTML = this._options.skipLabel;
    }

    //Set focus on "next" button, so that hitting Enter always moves you onto the next step
    nextTooltipButton.focus();

    //add target element position style
    targetElement.element.className += ' introjs-showElement';

    var currentElementPosition = _getPropValue(targetElement.element, 'position');
    if (currentElementPosition !== 'absolute' &&
        currentElementPosition !== 'relative') {
      //change to new intro item
      targetElement.element.className += ' introjs-relativePosition';
    }

    var parentElm = targetElement.element.parentNode;
    while (parentElm != null) {
      if (parentElm.tagName.toLowerCase() === 'body') break;

      //fix The Stacking Contenxt problem. 
      //More detail: https://developer.mozilla.org/en-US/docs/Web/Guide/CSS/Understanding_z_index/The_stacking_context
      var zIndex = _getPropValue(parentElm, 'z-index');
      var opacity = parseFloat(_getPropValue(parentElm, 'opacity'));
      if (/[0-9]+/.test(zIndex) || opacity < 1) {
        parentElm.className += ' introjs-fixParent';
      }
    
      parentElm = parentElm.parentNode;
    }

    if (!_elementInViewport(targetElement.element) && this._options.scrollToElement === true) {
      var rect = targetElement.element.getBoundingClientRect(),
        winHeight=_getWinSize().height,
        top = rect.bottom - (rect.bottom - rect.top),
        bottom = rect.bottom - winHeight;

      //Scroll up
      if (top < 0 || targetElement.element.clientHeight > winHeight) {
        window.scrollBy(0, top - 30); // 30px padding from edge to look nice

      //Scroll down
      } else {
        window.scrollBy(0, bottom + 100); // 70px + 30px padding from edge to look nice
      }
    }
    
    if (typeof (this._introAfterChangeCallback) !== 'undefined') {
        this._introAfterChangeCallback.call(this, targetElement.element);
    }
  }

  /**
   * Get an element CSS property on the page
   * Thanks to JavaScript Kit: http://www.javascriptkit.com/dhtmltutors/dhtmlcascade4.shtml
   *
   * @api private
   * @method _getPropValue
   * @param {Object} element
   * @param {String} propName
   * @returns Element's property value
   */
  function _getPropValue (element, propName) {
    var propValue = '';
    if (element.currentStyle) { //IE
      propValue = element.currentStyle[propName];
    } else if (document.defaultView && document.defaultView.getComputedStyle) { //Others
      propValue = document.defaultView.getComputedStyle(element, null).getPropertyValue(propName);
    }

    //Prevent exception in IE
    if (propValue && propValue.toLowerCase) {
      return propValue.toLowerCase();
    } else {
      return propValue;
    }
  }

  /**
   * Provides a cross-browser way to get the screen dimensions
   * via: http://stackoverflow.com/questions/5864467/internet-explorer-innerheight
   *
   * @api private
   * @method _getWinSize
   * @returns {Object} width and height attributes
   */
  function _getWinSize() {
    if (window.innerWidth != undefined) {
      return { width: window.innerWidth, height: window.innerHeight };
    } else {
      var D = document.documentElement;
      return { width: D.clientWidth, height: D.clientHeight };
    }
  }

  /**
   * Add overlay layer to the page
   * http://stackoverflow.com/questions/123999/how-to-tell-if-a-dom-element-is-visible-in-the-current-viewport
   *
   * @api private
   * @method _elementInViewport
   * @param {Object} el
   */
  function _elementInViewport(el) {
    var rect = el.getBoundingClientRect();

    return (
      rect.top >= 0 &&
      rect.left >= 0 &&
      (rect.bottom+80) <= window.innerHeight && // add 80 to get the text right
      rect.right <= window.innerWidth
    );
  }

  /**
   * Add overlay layer to the page
   *
   * @api private
   * @method _addOverlayLayer
   * @param {Object} targetElm
   */
  function _addOverlayLayer(targetElm) {
    var overlayLayer = document.createElement('div'),
        styleText = '',
        self = this;

    //set css class name
    overlayLayer.className = 'introjs-overlay';

    //check if the target element is body, we should calculate the size of overlay layer in a better way
    if (targetElm.tagName.toLowerCase() === 'body') {
      styleText += 'top: 0;bottom: 0; left: 0;right: 0;position: fixed;';
      overlayLayer.setAttribute('style', styleText);
    } else {
      //set overlay layer position
      var elementPosition = _getOffset(targetElm);
      if (elementPosition) {
        styleText += 'width: ' + elementPosition.width + 'px; height:' + elementPosition.height + 'px; top:' + elementPosition.top + 'px;left: ' + elementPosition.left + 'px;';
        overlayLayer.setAttribute('style', styleText);
      }
    }

    targetElm.appendChild(overlayLayer);

    overlayLayer.onclick = function() {
      if (self._options.exitOnOverlayClick == true) {
        _exitIntro.call(self, targetElm);

        //check if any callback is defined
        if (self._introExitCallback != undefined) {
          self._introExitCallback.call(self);
        }
      }
    };

    setTimeout(function() {
      styleText += 'opacity: .8;';
      overlayLayer.setAttribute('style', styleText);
    }, 10);
    return true;
  }

  /**
   * Get an element position on the page
   * Thanks to `meouw`: http://stackoverflow.com/a/442474/375966
   *
   * @api private
   * @method _getOffset
   * @param {Object} element
   * @returns Element's position info
   */
  function _getOffset(element) {
    var elementPosition = {};

    //set width
    elementPosition.width = element.offsetWidth;

    //set height
    elementPosition.height = element.offsetHeight;

    //calculate element top and left
    var _x = 0;
    var _y = 0;
    while (element && !isNaN(element.offsetLeft) && !isNaN(element.offsetTop)) {
      _x += element.offsetLeft;
      _y += element.offsetTop;
      element = element.offsetParent;
    }
    //set top
    elementPosition.top = _y;
    //set left
    elementPosition.left = _x;

    return elementPosition;
  }

  /**
   * Overwrites obj1's values with obj2's and adds obj2's if non existent in obj1
   * via: http://stackoverflow.com/questions/171251/how-can-i-merge-properties-of-two-javascript-objects-dynamically
   *
   * @param obj1
   * @param obj2
   * @returns obj3 a new object based on obj1 and obj2
   */
  function _mergeOptions(obj1,obj2) {
    var obj3 = {};
    for (var attrname in obj1) { obj3[attrname] = obj1[attrname]; }
    for (var attrname in obj2) { obj3[attrname] = obj2[attrname]; }
    return obj3;
  }

  var introJs = function (targetElm) {
    if (typeof (targetElm) === 'object') {
      //Ok, create a new instance
      return new IntroJs(targetElm);

    } else if (typeof (targetElm) === 'string') {
      //select the target element with query selector
      var targetElement = document.querySelector(targetElm);

      if (targetElement) {
        return new IntroJs(targetElement);
      } else {
        throw new Error('There is no element with given selector.');
      }
    } else {
      return new IntroJs(document.body);
    }
  };

  /**
   * Current IntroJs version
   *
   * @property version
   * @type String
   */
  introJs.version = VERSION;

  //Prototype
  introJs.fn = IntroJs.prototype = {
    clone: function () {
      return new IntroJs(this);
    },
    setOption: function(option, value) {
      this._options[option] = value;
      return this;
    },
    setOptions: function(options) {
      this._options = _mergeOptions(this._options, options);
      return this;
    },
    start: function () {
      _introForElement.call(this, this._targetElement);
      return this;
    },
    goToStep: function(step) {
      _goToStep.call(this, step);
      return this;
    },
    nextStep: function() {
      _nextStep.call(this);
      return this;
    },
    previousStep: function() {
      _previousStep.call(this);
      return this;
    },
    exit: function() {
      _exitIntro.call(this, this._targetElement);
    },
    refresh: function() {
      _setHelperLayerPosition.call(this, document.querySelector('.introjs-helperLayer'));
      return this;
    },
    onbeforechange: function(providedCallback) {
      if (typeof (providedCallback) === 'function') {
        this._introBeforeChangeCallback = providedCallback;
      } else {
        throw new Error('Provided callback for onbeforechange was not a function');
      }
      return this;
    },
    onchange: function(providedCallback) {
      if (typeof (providedCallback) === 'function') {
        this._introChangeCallback = providedCallback;
      } else {
        throw new Error('Provided callback for onchange was not a function.');
      }
      return this;
    },
    onafterchange: function(providedCallback) {
      if (typeof (providedCallback) === 'function') {
        this._introAfterChangeCallback = providedCallback;
      } else {
        throw new Error('Provided callback for onafterchange was not a function');
      }
      return this;
    },
    oncomplete: function(providedCallback) {
      if (typeof (providedCallback) === 'function') {
        this._introCompleteCallback = providedCallback;
      } else {
        throw new Error('Provided callback for oncomplete was not a function.');
      }
      return this;
    },
    onexit: function(providedCallback) {
      if (typeof (providedCallback) === 'function') {
        this._introExitCallback = providedCallback;
      } else {
        throw new Error('Provided callback for onexit was not a function.');
      }
      return this;
    }
  };

  exports.introJs = introJs;
  return introJs;
}));