dev/js/src/menu.js - KorAP/Kalamar - Gitiles

 /**
  * Scrollable drop-down menus with view filter.
  *
  * @author Nils Diewald
  */
 /*
  * TODO: space is not a valid prefix!
  * TODO: Show the slider briefly on move (whenever screen is called).
  * TODO: Optimize scrolling to active item.
  */
 define([
   'menu/item',
   'menu/prefix',
   'menu/lengthField',
   'menu/slider',
   'util'
 ], function (defaultItemClass,
 	     defaultPrefixClass,
 	     defaultLengthFieldClass,
 	     sliderClass) {

   // Default maximum number of menu items
   var menuLimit = 8;

   function _codeFromEvent (e) {
     if (e.charCode && (e.keyCode == 0))
       return e.charCode
     return e.keyCode;
   };


   /**
    * List of items for drop down menu (complete).
    * Only a sublist of the menu is filtered (live).
    * Only a sublist of the filtered menu is visible (shown).
    */
   return {
     /**
      * Create new Menu based on the action prefix
      * and a list of menu items.
      *
      * @this {Menu}
      * @constructor
      * @param {string} Context prefix
      * @param {Array.<Array.<string>>} List of menu items
      */
     create : function (params) {
       return Object.create(this)._init(params);
     },

     // Initialize list
     _init : function (itemClass, prefixClass, lengthFieldClass, params) {

       this._itemClass = itemClass || defaultItemClass;

       // Add prefix object
       if (prefixClass !== undefined) {
 	this._prefix = prefixClass.create();
       }
       else {
 	this._prefix = defaultPrefixClass.create();
       };
       this._prefix._menu = this;

       // Add lengthField object
       if (lengthFieldClass !== undefined) {
 	this._lengthField = lengthFieldClass.create();
       }
       else {
 	this._lengthField = defaultLengthFieldClass.create();
       };
       this._lengthField._menu = this;

       // Initialize slider
       this._slider = sliderClass.create(this);

       // Create the element
       var e = document.createElement("ul");
       e.style.opacity = 0;
       e.style.outline = 0;
       e.setAttribute('tabindex', 0);
       e.classList.add('menu');
       e.classList.add('roll');
       e.appendChild(this._prefix.element());
       e.appendChild(this._lengthField.element());
       e.appendChild(this._slider.element());

       // This has to be cleaned up later on
       e["menu"] = this;

       // Arrow keys
       e.addEventListener(
 	'keydown',
 	this._keydown.bind(this),
 	false
       );

       // Strings
       e.addEventListener(
 	'keypress',
 	this._keypress.bind(this),
 	false
       );

       // Mousewheel
       e.addEventListener(
 	'wheel',
 	this._mousewheel.bind(this),
 	false
       );

       this._element = e;
       this.active = false;
       // this.selected = undefined;
       this._items = new Array();
       var i = 0;

       // Initialize item list based on parameters
       for (i in params) {
 	var obj = this._itemClass.create(params[i]);

 	// This may become circular
 	obj["_menu"] = this;
 	this._lengthField.add(params[i]);
 	this._items.push(obj);
       };

       this._limit    = menuLimit;
       this._slider.length(this.liveLength());
       this._slider.limit(this._limit);

       this._firstActive = false; // Show the first item active always?
       this._reset();
       return this;
     },

     // Initialize the item list
     _initList : function () {

       // Create a new list
       if (this._list === undefined) {
 	this._list = [];
       }
       else if (this._list.length !== 0) {
 	this._boundary(false);
 	this._list.length = 0;
       };

       // Offset is initially zero
       this._offset = 0;

       // There is no prefix set
       if (this.prefix().length <= 0) {

 	// add all items to the list and lowlight
 	var i = 0;
 	for (; i < this._items.length; i++) {
 	  this._list.push(i);
 	  this._items[i].lowlight();
 	};

 	this._slider.length(i);

 	return true;
       };

       /*
        * There is a prefix set, so filter the list!
        */
       var pos;
       var prefix = " " + this.prefix().toLowerCase();

       // Iterate over all items and choose preferred matching items
       // i.e. the matching happens at the word start
       for (pos = 0; pos < this._items.length; pos++) {
 	if ((this.item(pos).lcField().indexOf(prefix)) >= 0)
 	  this._list.push(pos);
       };

       // The list is empty - so lower your expectations
       // Iterate over all items and choose matching items
       // i.e. the matching happens anywhere in the word
       prefix = prefix.substring(1);
       if (this._list.length == 0) {
 	for (pos = 0; pos < this._items.length; pos++) {
 	  if ((this.item(pos).lcField().indexOf(prefix)) >= 0)
 	    this._list.push(pos);
 	};
       };

       this._slider.length(this._list.length);

       // Filter was successful - yeah!
       return this._list.length > 0 ? true : false;
     },


     /**
      * Destroy this menu
      * (in case you don't trust the
      * mark and sweep GC)!
      */
     destroy : function () {

       // Remove circular reference to "this" in menu
       if (this._element != undefined)
 	delete this._element["menu"];

       // Remove circular reference to "this" in items
       for (var i = 0; i < this._items.length; i++) {
 	delete this._items[i]["_menu"];
       };

       // Remove circular reference to "this" in prefix
       delete this._prefix['_menu'];
       delete this._lengthField['_menu'];
       delete this._slider['_menu'];
     },


     /**
      * Focus on this menu.
      */
     focus : function () {
       this._element.focus();
     },


     // mouse wheel treatment
     _mousewheel : function (e) {
       var delta = 0;

       delta = e.deltaY / 120;
       if (delta > 0)
 	this.next();
       else if (delta < 0)
 	this.prev();
       e.halt();
     },


     // Arrow key and prefix treatment
     _keydown : function (e) {
       var code = _codeFromEvent(e);

       switch (code) {
       case 27: // 'Esc'
 	e.halt();
 	this.hide();
 	break;

       case 38: // 'Up'
 	e.halt();
 	this.prev();
 	break;
       case 33: // 'Page up'
 	e.halt();
 	this.pageUp();
 	break;
       case 40: // 'Down'
 	e.halt();
 	this.next();
 	break;
       case 34: // 'Page down'
 	e.halt();
 	this.pageDown();
 	break;
       case 39: // 'Right'
 	if (this._prefix.active())
 	  break;

 	var item = this.liveItem(this.position);

 	if (item["further"] !== undefined) {
 	  item["further"].bind(item).apply();
 	};

 	e.halt();
 	break;
       case 13: // 'Enter'

 	// Click on prefix
 	if (this._prefix.active())
 	  this._prefix.onclick(e);

 	// Click on item
 	else
 	  this.liveItem(this.position).onclick(e);
 	e.halt();
 	break;
       case 8: // 'Backspace'
 	this._prefix.chop();
 	this.show();
 	e.halt();
 	break;
       };
     },

     // Add characters to prefix
     _keypress : function (e) {
       if (e.charCode !== 0) {
 	e.halt();
 	var c = String.fromCharCode(_codeFromEvent(e));

 	// Add prefix
 	this._prefix.add(c);
 	this.show();
       };
     },

     /**
      * Show a screen with a given offset
      * in the viewport.
      */
     screen : function (nr) {
       if (nr < 0) {
 	nr = 0
       }
       else if (nr > (this.liveLength() - this.limit())) {
 	nr = (this.liveLength() - this.limit());
       };

       if (this._offset === nr)
 	return;

       this._showItems(nr);
     },

     /**
      * Get the associated dom element.
      */
     element : function () {
       return this._element;
     },

     /**
      * Get the creator class for items
      */
     itemClass : function () {
       return this._itemClass;
     },

     /**
      * Get and set the numerical value
      * for the maximum number of items visible.
      */
     limit : function (limit) {
       if (arguments.length === 1) {
 	if (this._limit !== limit) {
 	  this._limit = limit;
 	  this._slider.limit(limit);
 	};
 	return this;
       };
       return this._limit;
     },


     /**
      * Upgrade this object to another object,
      * while private data stays intact.
      *
      * @param {Object} An object with properties.
      */
     upgradeTo : function (props) {
       for (var prop in props) {
 	this[prop] = props[prop];
       };
       return this;
     },


     /**
      * Filter the list and make it visible.
      * This is always called once the prefix changes.
      *
      * @param {string} Prefix for filtering the list
      */
     show : function (active) {

       // show menu based on initial offset
       this._unmark();     // Unmark everything that was marked before
       this.removeItems();

       // Initialize the list
       if (!this._initList()) {

 	// The prefix is not active
 	this._prefix.active(true);

 	// finally show the element
 	this._element.style.opacity = 1;

 	return true;
       };

       var offset = 0;


       // Set a chosen value to active and move the viewport
       if (arguments.length === 1) {

 	// Normalize active value
 	if (active < 0) {
 	  active = 0;
 	}
 	else if (active > this.liveLength()) {
 	  active = this.liveLength() - 1;
 	};

 	if (active > this._limit) {
 	  offset = active;
 	  if (offset > (this.liveLength() - this._limit)) {
 	      offset = this.liveLength() - this._limit;
 	  };
 	};

 	this.position = active;
       }

       // Choose the first item
       else if (this._firstActive) {
 	this.position = 0;
       }

       // Choose no item
       else {
 	this.position = -1;
       };

       this._offset = offset;
       this._showItems(offset); // Show new item list

       // Make chosen value active
       if (this.position !== -1) {
 	this.liveItem(this.position).active(true);
       };

       // The prefix is not active
       this._prefix.active(false);

       // finally show the element
       this._element.style.opacity = 1;

       // Add classes for rolling menus
       this._boundary(true);
       return true;
     },


     /**
      * Hide the menu and call the onHide callback.
      */
     hide : function () {
       this.active = false;
       this._unmark();
       this.removeItems();
       this._element.style.opacity = 0;
       this._prefix.clear();
       this.onHide();
       /* this._element.blur(); */
     },

     /**
      * Function released when the menu hides.
      * This method is expected to be overridden.
      */
     onHide : function () {},


     /**
      * Get the prefix for filtering,
      * e.g. &quot;ve&quot; for &quot;verb&quot;
      */
     prefix : function (pref) {
       if (arguments.length === 1) {
 	this._prefix.value(pref);
 	return this;
       };
       return this._prefix.value();
     },

     /**
      * Get the lengthField object.
      */
     lengthField : function () {
       return this._lengthField;
     },

     /**
      * Get the associated slider object.
      */
     slider : function () {
       return this._slider;
     },


     /**
      * Delete all visible items from the menu element
      */
     removeItems : function () {
       var child;

       // Remove all children
       var children = this._element.childNodes;
       // Leave the prefix and lengthField
       for (var i = children.length - 1; i >= 3; i--) {
 	this._element.removeChild(
 	  children[i]
 	);
       };
     },

     /**
      * Get a specific item from the complete list
      *
      * @param {number} index of the list item
      */
     item : function (index) {
       return this._items[index]
     },


     /**
      * Get a specific item from the filtered list
      *
      * @param {number} index of the list item
      *        in the filtered list
      */
     liveItem : function (index) {
       if (this._list === undefined)
 	if (!this._initList())
 	  return;

       return this._items[this._list[index]];
     },


     /**
      * Get a specific item from the viewport list
      *
      * @param {number} index of the list item
      *        in the visible list
      */
     shownItem : function (index) {
       if (index >= this.limit())
 	return;
       return this.liveItem(this._offset + index);
     },


     /**
      * Get the length of the full list
      */
     length : function () {
       return this._items.length;
     },


     /**
      * Length of the filtered item list.
      */
     liveLength : function () {
       if (this._list === undefined)
 	this._initList();
       return this._list.length;
     },


     /**
      * Make the next item in the filtered menu active
      */
     next : function () {

       // No active element set
       var newItem;

       if (this.position !== -1) {
 	// Set new live item
 	if (!this._prefix.active()) {
 	  var oldItem = this.liveItem(this.position);
 	  oldItem.active(false);
 	};
       };

       // No list
       if (this.liveLength() === 0)
 	return;

       this.position++;

       newItem = this.liveItem(this.position);

       // The next element is undefined - roll to top or to prefix
       if (newItem === undefined) {

 	// Activate prefix
 	var prefix = this._prefix;

 	// Mark prefix
 	if (prefix.isSet() && !prefix.active()) {
 	  this.position--;
 	  prefix.active(true);
 	  return;
 	}
 	else {
 	  this.position = 0;
 	  newItem = this.liveItem(0);
 	  this._showItems(0);
 	};
       }

       // The next element is after the viewport - roll down
       else if (this.position >= (this.limit() + this._offset)) {
 	this.screen(this.position - this.limit() + 1);
       }

       // The next element is before the viewport - roll up
       else if (this.position <= this._offset) {
 	this.screen(this.position);
       };

       this._prefix.active(false);
       newItem.active(true);
     },

     /*
      * Make the previous item in the menu active
      */
     prev : function () {

       // No active element set
       if (this.position === -1) {
 	// TODO: Choose last item
 	return;
       };

       // No list
       if (this.liveLength() === 0)
 	return;

       var newItem;

       // Set new live item
       if (!this._prefix.active()) {
 	var oldItem = this.liveItem(this.position--);
 	oldItem.active(false);
       };

       newItem = this.liveItem(this.position);

       // The previous element is undefined - roll to bottom
       if (newItem === undefined) {

 	// Activate prefix
 	var prefix = this._prefix;
 	var offset =  this.liveLength() - this.limit();
 	// this._offset = this.liveLength() - this.limit();

 	// Normalize offset
 	// this._offset = this._offset < 0 ? 0 : this._offset;
 	offset = offset < 0 ? 0 : offset;

 	this.position = this.liveLength() - 1;

 	if (prefix.isSet() && !prefix.active()) {
 	  this.position++;
 	  prefix.active(true);
 	  this._offset = offset;
 	  return;
 	}
 	else {
 	  newItem = this.liveItem(this.position);
 	  this._unmark();
 	  this._showItems(offset);
 	};
       }

       // The previous element is before the view - roll up
       else if (this.position < this._offset) {
 	this.screen(this.position);
       }

       // The previous element is after the view - roll down
       else if (this.position >= (this.limit() + this._offset)) {
 	this.screen(this.position - this.limit() + 2);
       };

       this._prefix.active(false);
       newItem.active(true);
     },

     /**
      * Move the page up by limit!
      */
     pageUp : function () {
       this.screen(this._offset - this.limit());
     },


     /**
      * Move the page down by limit!
      */
     pageDown : function () {
       this.screen(this._offset + this.limit());
     },


     // Unmark all items
     _unmark : function () {
       for (var i in this._list) {
 	var item = this._items[this._list[i]];
 	item.lowlight();
 	item.active(false);
       };
     },


     // Reset chosen item and prefix
     _reset : function () {
       this._offset = 0;
       this.position = 0;
       this._prefix.clear();
     },


     // Set boundary for viewport
     _boundary : function (bool) {
       this.item(this._list[0]).noMore(bool);
       this.item(this._list[this._list.length - 1]).noMore(bool);
     },


     // Append Items that should be shown
     _showItems : function (off) {

       // optimization: scroll down one step
       if (this._offset === (off - 1)) {
 	this._offset = off;
 	this._removeFirst();
 	var pos = this._offset + this.limit() - 1;
 	this._append(this._list[pos]);
       }

       // optimization: scroll up one step
       else if (this._offset === (off + 1)) {
 	this._offset = off;
 	this._removeLast();
 	this._prepend(this._list[this._offset]);
       }
       else {
 	this._offset = off;

 	// Remove all items
 	this.removeItems();

 	// Use list
 	var shown = 0;
 	var i;

 	for (i in this._list) {

 	  // Don't show - it's before offset
 	  shown++;
 	  if (shown <= off)
 	    continue;

 	  var itemNr = this._list[i];
 	  var item = this.item(itemNr);
 	  this._append(itemNr);

 	  if (shown >= (this.limit() + off))
 	    break;
 	};
       };

       // set the slider to the new offset
       this._slider.offset(this._offset);
     },


     // Append item to the shown list based on index
     _append : function (i) {
       var item = this.item(i);

       // Highlight based on prefix
       if (this.prefix().length > 0) {
 	item.highlight(this.prefix().toLowerCase());
       };


       // Append element
       this.element().appendChild(item.element());
     },


     // Prepend item to the shown list based on index
     _prepend : function (i) {
       var item = this.item(i);

       // Highlight based on prefix
       if (this.prefix().length > 0) {
 	item.highlight(this.prefix().toLowerCase());
       };

       var e = this.element();
       // Append element after lengthField/prefix/slider
       e.insertBefore(
 	item.element(),
 	e.children[3]
       );
     },


     // Remove the HTML node from the first item
     _removeFirst : function () {
       // this.item(this._list[this._offset]).lowlight();
       // leave lengthField/prefix/slider
       this._element.removeChild(this._element.children[3]);
     },


     // Remove the HTML node from the last item
     _removeLast : function () {
       // this.item(this._list[this._offset + this.limit() - 1]).lowlight();
       this._element.removeChild(this._element.lastChild);
     }
   };
 });
	/**
	* Scrollable drop-down menus with view filter.
	*
	* @author Nils Diewald
	*/
	/*
	* TODO: space is not a valid prefix!
	* TODO: Show the slider briefly on move (whenever screen is called).
	* TODO: Optimize scrolling to active item.
	*/
	define([
	'menu/item',
	'menu/prefix',
	'menu/lengthField',
	'menu/slider',
	'util'
	], function (defaultItemClass,
	defaultPrefixClass,
	defaultLengthFieldClass,
	sliderClass) {

	// Default maximum number of menu items
	var menuLimit = 8;

	function _codeFromEvent (e) {
	if (e.charCode && (e.keyCode == 0))
	return e.charCode
	return e.keyCode;
	};


	/**
	* List of items for drop down menu (complete).
	* Only a sublist of the menu is filtered (live).
	* Only a sublist of the filtered menu is visible (shown).
	*/
	return {
	/**
	* Create new Menu based on the action prefix
	* and a list of menu items.
	*
	* @this {Menu}
	* @constructor
	* @param {string} Context prefix
	* @param {Array.<Array.<string>>} List of menu items
	*/
	create : function (params) {
	return Object.create(this)._init(params);
	},

	// Initialize list
	_init : function (itemClass, prefixClass, lengthFieldClass, params) {

	this._itemClass = itemClass \|\| defaultItemClass;

	// Add prefix object
	if (prefixClass !== undefined) {
	this._prefix = prefixClass.create();
	}
	else {
	this._prefix = defaultPrefixClass.create();
	};
	this._prefix._menu = this;

	// Add lengthField object
	if (lengthFieldClass !== undefined) {
	this._lengthField = lengthFieldClass.create();
	}
	else {
	this._lengthField = defaultLengthFieldClass.create();
	};
	this._lengthField._menu = this;

	// Initialize slider
	this._slider = sliderClass.create(this);

	// Create the element
	var e = document.createElement("ul");
	e.style.opacity = 0;
	e.style.outline = 0;
	e.setAttribute('tabindex', 0);
	e.classList.add('menu');
	e.classList.add('roll');
	e.appendChild(this._prefix.element());
	e.appendChild(this._lengthField.element());
	e.appendChild(this._slider.element());

	// This has to be cleaned up later on
	e["menu"] = this;

	// Arrow keys
	e.addEventListener(
	'keydown',
	this._keydown.bind(this),
	false
	);

	// Strings
	e.addEventListener(
	'keypress',
	this._keypress.bind(this),
	false
	);

	// Mousewheel
	e.addEventListener(
	'wheel',
	this._mousewheel.bind(this),
	false
	);

	this._element = e;
	this.active = false;
	// this.selected = undefined;
	this._items = new Array();
	var i = 0;

	// Initialize item list based on parameters
	for (i in params) {
	var obj = this._itemClass.create(params[i]);

	// This may become circular
	obj["_menu"] = this;
	this._lengthField.add(params[i]);
	this._items.push(obj);
	};

	this._limit = menuLimit;
	this._slider.length(this.liveLength());
	this._slider.limit(this._limit);

	this._firstActive = false; // Show the first item active always?
	this._reset();
	return this;
	},

	// Initialize the item list
	_initList : function () {

	// Create a new list
	if (this._list === undefined) {
	this._list = [];
	}
	else if (this._list.length !== 0) {
	this._boundary(false);
	this._list.length = 0;
	};

	// Offset is initially zero
	this._offset = 0;

	// There is no prefix set
	if (this.prefix().length <= 0) {

	// add all items to the list and lowlight
	var i = 0;
	for (; i < this._items.length; i++) {
	this._list.push(i);
	this._items[i].lowlight();
	};

	this._slider.length(i);

	return true;
	};

	/*
	* There is a prefix set, so filter the list!
	*/
	var pos;
	var prefix = " " + this.prefix().toLowerCase();

	// Iterate over all items and choose preferred matching items
	// i.e. the matching happens at the word start
	for (pos = 0; pos < this._items.length; pos++) {
	if ((this.item(pos).lcField().indexOf(prefix)) >= 0)
	this._list.push(pos);
	};

	// The list is empty - so lower your expectations
	// Iterate over all items and choose matching items
	// i.e. the matching happens anywhere in the word
	prefix = prefix.substring(1);
	if (this._list.length == 0) {
	for (pos = 0; pos < this._items.length; pos++) {
	if ((this.item(pos).lcField().indexOf(prefix)) >= 0)
	this._list.push(pos);
	};
	};

	this._slider.length(this._list.length);

	// Filter was successful - yeah!
	return this._list.length > 0 ? true : false;
	},


	/**
	* Destroy this menu
	* (in case you don't trust the
	* mark and sweep GC)!
	*/
	destroy : function () {

	// Remove circular reference to "this" in menu
	if (this._element != undefined)
	delete this._element["menu"];

	// Remove circular reference to "this" in items
	for (var i = 0; i < this._items.length; i++) {
	delete this._items[i]["_menu"];
	};

	// Remove circular reference to "this" in prefix
	delete this._prefix['_menu'];
	delete this._lengthField['_menu'];
	delete this._slider['_menu'];
	},


	/**
	* Focus on this menu.
	*/
	focus : function () {
	this._element.focus();
	},


	// mouse wheel treatment
	_mousewheel : function (e) {
	var delta = 0;

	delta = e.deltaY / 120;
	if (delta > 0)
	this.next();
	else if (delta < 0)
	this.prev();
	e.halt();
	},


	// Arrow key and prefix treatment
	_keydown : function (e) {
	var code = _codeFromEvent(e);

	switch (code) {
	case 27: // 'Esc'
	e.halt();
	this.hide();
	break;

	case 38: // 'Up'
	e.halt();
	this.prev();
	break;
	case 33: // 'Page up'
	e.halt();
	this.pageUp();
	break;
	case 40: // 'Down'
	e.halt();
	this.next();
	break;
	case 34: // 'Page down'
	e.halt();
	this.pageDown();
	break;
	case 39: // 'Right'
	if (this._prefix.active())
	break;

	var item = this.liveItem(this.position);

	if (item["further"] !== undefined) {
	item["further"].bind(item).apply();
	};

	e.halt();
	break;
	case 13: // 'Enter'

	// Click on prefix
	if (this._prefix.active())
	this._prefix.onclick(e);

	// Click on item
	else
	this.liveItem(this.position).onclick(e);
	e.halt();
	break;
	case 8: // 'Backspace'
	this._prefix.chop();
	this.show();
	e.halt();
	break;
	};
	},

	// Add characters to prefix
	_keypress : function (e) {
	if (e.charCode !== 0) {
	e.halt();
	var c = String.fromCharCode(_codeFromEvent(e));

	// Add prefix
	this._prefix.add(c);
	this.show();
	};
	},

	/**
	* Show a screen with a given offset
	* in the viewport.
	*/
	screen : function (nr) {
	if (nr < 0) {
	nr = 0
	}
	else if (nr > (this.liveLength() - this.limit())) {
	nr = (this.liveLength() - this.limit());
	};

	if (this._offset === nr)
	return;

	this._showItems(nr);
	},

	/**
	* Get the associated dom element.
	*/
	element : function () {
	return this._element;
	},

	/**
	* Get the creator class for items
	*/
	itemClass : function () {
	return this._itemClass;
	},

	/**
	* Get and set the numerical value
	* for the maximum number of items visible.
	*/
	limit : function (limit) {
	if (arguments.length === 1) {
	if (this._limit !== limit) {
	this._limit = limit;
	this._slider.limit(limit);
	};
	return this;
	};
	return this._limit;
	},


	/**
	* Upgrade this object to another object,
	* while private data stays intact.
	*
	* @param {Object} An object with properties.
	*/
	upgradeTo : function (props) {
	for (var prop in props) {
	this[prop] = props[prop];
	};
	return this;
	},


	/**
	* Filter the list and make it visible.
	* This is always called once the prefix changes.
	*
	* @param {string} Prefix for filtering the list
	*/
	show : function (active) {

	// show menu based on initial offset
	this._unmark(); // Unmark everything that was marked before
	this.removeItems();

	// Initialize the list
	if (!this._initList()) {

	// The prefix is not active
	this._prefix.active(true);

	// finally show the element
	this._element.style.opacity = 1;

	return true;
	};

	var offset = 0;


	// Set a chosen value to active and move the viewport
	if (arguments.length === 1) {

	// Normalize active value
	if (active < 0) {
	active = 0;
	}
	else if (active > this.liveLength()) {
	active = this.liveLength() - 1;
	};

	if (active > this._limit) {
	offset = active;
	if (offset > (this.liveLength() - this._limit)) {
	offset = this.liveLength() - this._limit;
	};
	};

	this.position = active;
	}

	// Choose the first item
	else if (this._firstActive) {
	this.position = 0;
	}

	// Choose no item
	else {
	this.position = -1;
	};

	this._offset = offset;
	this._showItems(offset); // Show new item list

	// Make chosen value active
	if (this.position !== -1) {
	this.liveItem(this.position).active(true);
	};

	// The prefix is not active
	this._prefix.active(false);

	// finally show the element
	this._element.style.opacity = 1;

	// Add classes for rolling menus
	this._boundary(true);
	return true;
	},


	/**
	* Hide the menu and call the onHide callback.
	*/
	hide : function () {
	this.active = false;
	this._unmark();
	this.removeItems();
	this._element.style.opacity = 0;
	this._prefix.clear();
	this.onHide();
	/* this._element.blur(); */
	},

	/**
	* Function released when the menu hides.
	* This method is expected to be overridden.
	*/
	onHide : function () {},


	/**
	* Get the prefix for filtering,
	* e.g. "ve" for "verb"
	*/
	prefix : function (pref) {
	if (arguments.length === 1) {
	this._prefix.value(pref);
	return this;
	};
	return this._prefix.value();
	},

	/**
	* Get the lengthField object.
	*/
	lengthField : function () {
	return this._lengthField;
	},

	/**
	* Get the associated slider object.
	*/
	slider : function () {
	return this._slider;
	},


	/**
	* Delete all visible items from the menu element
	*/
	removeItems : function () {
	var child;

	// Remove all children
	var children = this._element.childNodes;
	// Leave the prefix and lengthField
	for (var i = children.length - 1; i >= 3; i--) {
	this._element.removeChild(
	children[i]
	);
	};
	},

	/**
	* Get a specific item from the complete list
	*
	* @param {number} index of the list item
	*/
	item : function (index) {
	return this._items[index]
	},


	/**
	* Get a specific item from the filtered list
	*
	* @param {number} index of the list item
	* in the filtered list
	*/
	liveItem : function (index) {
	if (this._list === undefined)
	if (!this._initList())
	return;

	return this._items[this._list[index]];
	},


	/**
	* Get a specific item from the viewport list
	*
	* @param {number} index of the list item
	* in the visible list
	*/
	shownItem : function (index) {
	if (index >= this.limit())
	return;
	return this.liveItem(this._offset + index);
	},


	/**
	* Get the length of the full list
	*/
	length : function () {
	return this._items.length;
	},


	/**
	* Length of the filtered item list.
	*/
	liveLength : function () {
	if (this._list === undefined)
	this._initList();
	return this._list.length;
	},


	/**
	* Make the next item in the filtered menu active
	*/
	next : function () {

	// No active element set
	var newItem;

	if (this.position !== -1) {
	// Set new live item
	if (!this._prefix.active()) {
	var oldItem = this.liveItem(this.position);
	oldItem.active(false);
	};
	};

	// No list
	if (this.liveLength() === 0)
	return;

	this.position++;

	newItem = this.liveItem(this.position);

	// The next element is undefined - roll to top or to prefix
	if (newItem === undefined) {

	// Activate prefix
	var prefix = this._prefix;

	// Mark prefix
	if (prefix.isSet() && !prefix.active()) {
	this.position--;
	prefix.active(true);
	return;
	}
	else {
	this.position = 0;
	newItem = this.liveItem(0);
	this._showItems(0);
	};
	}

	// The next element is after the viewport - roll down
	else if (this.position >= (this.limit() + this._offset)) {
	this.screen(this.position - this.limit() + 1);
	}

	// The next element is before the viewport - roll up
	else if (this.position <= this._offset) {
	this.screen(this.position);
	};

	this._prefix.active(false);
	newItem.active(true);
	},

	/*
	* Make the previous item in the menu active
	*/
	prev : function () {

	// No active element set
	if (this.position === -1) {
	// TODO: Choose last item
	return;
	};

	// No list
	if (this.liveLength() === 0)
	return;

	var newItem;

	// Set new live item
	if (!this._prefix.active()) {
	var oldItem = this.liveItem(this.position--);
	oldItem.active(false);
	};

	newItem = this.liveItem(this.position);

	// The previous element is undefined - roll to bottom
	if (newItem === undefined) {

	// Activate prefix
	var prefix = this._prefix;
	var offset = this.liveLength() - this.limit();
	// this._offset = this.liveLength() - this.limit();

	// Normalize offset
	// this._offset = this._offset < 0 ? 0 : this._offset;
	offset = offset < 0 ? 0 : offset;

	this.position = this.liveLength() - 1;

	if (prefix.isSet() && !prefix.active()) {
	this.position++;
	prefix.active(true);
	this._offset = offset;
	return;
	}
	else {
	newItem = this.liveItem(this.position);
	this._unmark();
	this._showItems(offset);
	};
	}

	// The previous element is before the view - roll up
	else if (this.position < this._offset) {
	this.screen(this.position);
	}

	// The previous element is after the view - roll down
	else if (this.position >= (this.limit() + this._offset)) {
	this.screen(this.position - this.limit() + 2);
	};

	this._prefix.active(false);
	newItem.active(true);
	},

	/**
	* Move the page up by limit!
	*/
	pageUp : function () {
	this.screen(this._offset - this.limit());
	},


	/**
	* Move the page down by limit!
	*/
	pageDown : function () {
	this.screen(this._offset + this.limit());
	},


	// Unmark all items
	_unmark : function () {
	for (var i in this._list) {
	var item = this._items[this._list[i]];
	item.lowlight();
	item.active(false);
	};
	},


	// Reset chosen item and prefix
	_reset : function () {
	this._offset = 0;
	this.position = 0;
	this._prefix.clear();
	},


	// Set boundary for viewport
	_boundary : function (bool) {
	this.item(this._list[0]).noMore(bool);
	this.item(this._list[this._list.length - 1]).noMore(bool);
	},


	// Append Items that should be shown
	_showItems : function (off) {

	// optimization: scroll down one step
	if (this._offset === (off - 1)) {
	this._offset = off;
	this._removeFirst();
	var pos = this._offset + this.limit() - 1;
	this._append(this._list[pos]);
	}

	// optimization: scroll up one step
	else if (this._offset === (off + 1)) {
	this._offset = off;
	this._removeLast();
	this._prepend(this._list[this._offset]);
	}
	else {
	this._offset = off;

	// Remove all items
	this.removeItems();

	// Use list
	var shown = 0;
	var i;

	for (i in this._list) {

	// Don't show - it's before offset
	shown++;
	if (shown <= off)
	continue;

	var itemNr = this._list[i];
	var item = this.item(itemNr);
	this._append(itemNr);

	if (shown >= (this.limit() + off))
	break;
	};
	};

	// set the slider to the new offset
	this._slider.offset(this._offset);
	},


	// Append item to the shown list based on index
	_append : function (i) {
	var item = this.item(i);

	// Highlight based on prefix
	if (this.prefix().length > 0) {
	item.highlight(this.prefix().toLowerCase());
	};


	// Append element
	this.element().appendChild(item.element());
	},


	// Prepend item to the shown list based on index
	_prepend : function (i) {
	var item = this.item(i);

	// Highlight based on prefix
	if (this.prefix().length > 0) {
	item.highlight(this.prefix().toLowerCase());
	};

	var e = this.element();
	// Append element after lengthField/prefix/slider
	e.insertBefore(
	item.element(),
	e.children[3]
	);
	},


	// Remove the HTML node from the first item
	_removeFirst : function () {
	// this.item(this._list[this._offset]).lowlight();
	// leave lengthField/prefix/slider
	this._element.removeChild(this._element.children[3]);
	},


	// Remove the HTML node from the last item
	_removeLast : function () {
	// this.item(this._list[this._offset + this.limit() - 1]).lowlight();
	this._element.removeChild(this._element.lastChild);
	}
	};
	});