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  1. +3 −0  LICENSE
  2. +32 −1 README.md
  3. +287 −0 jquery.stalker.js
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3  LICENSE
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+This software is licensed under the Apache 2.0 license. This includes all files created by the authors in this distribution. This project includes work from third parties as well. Third party included files fall under their own license terms.
+
+The full text of the license agreement is at http://www.apache.org/licenses/LICENSE-2.0
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33 README.md
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stalker
=======
-A jQuery plugin allowing elements to follow the user as they scroll a page.
+A jQuery plugin allowing elements to follow the user as they scroll a page.
+
+Usage
+-----
+
+```js
+$(elements).stalker()
+```
+
+Parameters
+-----
+
+**direction** (string - default: 'down'):
+The direction the element should follow the user from its original position. For example, specifying 'up' means that whenever the user is scrolled above the element's original position, the element will follow the user along the page. When the user scrolls beneath the element's original position, the element will return to that position.
+
+**offset** (integer - default: 0):
+The number of pixels from the edge of the screen the element should position itself while following the user.
+
+**stalkerStyle** (object/string - default: {}):
+CSS properties to be applied to the element while it is following the user. The element's original CSS will be saved and reapplied when it returns to its original position. If a string is given, it will be treated as a class to apply to the element while it is following the user.
+
+**delay** (integer - default: 0):
+The delay, in milliseconds, before the element leaves its original position to follow the user. _Note: if animation is enabled, this will default to 300, as setting it too short doesn't look very good._
+
+**animate** (boolean - default: false):
+Whether or not to animate the stalking element into position. If set to true, the element will slide into its position at the edge of the page.
+
+**startCallback** (function - default: none):
+A callback to be executed when the element begins following the user. The function context will be the DOM element which is starting to follow.
+
+**stopCallback** (function - default: none):
+A callback to be executed as soon as the element stops following the user and returns to its original position. The function context will be the DOM element which is no longer following.
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287 jquery.stalker.js
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+/*
+ * Project: Stalker jQuery plugin
+ * Description: Allowing elements to follow the user as the scroll around the page in a
+ * single direction
+ * Version: 1.0 (Sep 9, 2012)
+ * Author: Matt Willer, Box Inc (http://www.box.com)
+ * License: BSD
+ *
+ *
+ * Usage:
+ * JS -
+ * $(elements).stalker()
+ *
+ * Optional params:
+ * direction (string - default: 'down') -
+ * The direction the element should follow the user from its original position. For
+ * example, specifying 'up' means that whenever the user is scrolled above the
+ * element's original position, the element will follow the user along the page.
+ * When the user scrolls beneath the element's original position, the element will
+ * return to that position.
+ * offset (integer - default: 0) -
+ * The number of pixels from the edge of the screen the element should position itself
+ * while following the user.
+ * stalkerStyle (object/string - default: {}) -
+ * CSS properties to be applied to the element while it is following the user. The
+ * element's original CSS will be saved and reapplied when it returns to its original
+ * position. If a string is given, it will be treated as a class to apply to the
+ * element while it is following the user.
+ * delay (integer - default: 0) -
+ * The delay, in milliseconds, before the element leaves its original position to
+ * follow the user. Note: if animation is enabled, this will default to 300, as
+ * setting it too short looks bad
+ * animate (boolean - default: false) -
+ * Whether or not to animate the stalking element into position. If set to true, the
+ * element will slide into its position at the edge of the page.
+ * startCallback (function - default: none) -
+ * A callback to be executed when the element begins following the user. The function
+ * context will be the DOM element
+ * stopCallback (function - default: none) -
+ * A callback to be executed as soon as the element stops following the user and
+ * returns to its original position. The function context will be the DOM element
+ *
+*/
+
+// the semi-colon before function invocation is a safety net against concatenated
+// scripts and/or other plugins which may not be closed properly.
+;(function ( $, window, undefined ) {
+
+ // undefined is used here as the undefined global variable in ECMAScript 3 is
+ // mutable (ie. it can be changed by someone else). undefined isn't really being
+ // passed in so we can ensure the value of it is truly undefined. In ES5, undefined
+ // can no longer be modified.
+
+ // window and document are passed through as local variables rather than globals
+ // as this (slightly) quickens the resolution process and can be more efficiently
+ // minified (especially when both are regularly referenced in your plugin).
+
+ // Create the defaults once
+ var pluginName = 'stalker'
+ ,document = window.document
+ ,defaults = {
+ direction: 'down'
+ ,offset: 0
+ ,stalkerStyle: {}
+ ,delay: 0
+ ,animate: false
+ ,startCallback: null
+ ,stopCallback: null
+ }
+ // change this to fit the CSS of the site if necessary
+ ,stalkerZIndex = 50;
+
+ // The actual plugin constructor
+ function Stalker( element, options )
+ {
+ this.element = element;
+
+ if (options && options.animate && options.delay == undefined)
+ {
+ // if animation is turned on without specifying a delay, set a sane one
+ options.delay = 300;
+ }
+
+ // jQuery has an extend method which merges the contents of two or
+ // more objects, storing the result in the first object. The first object
+ // is generally empty as we don't want to alter the default options for
+ // future instances of the plugin
+ this.options = $.extend( {}, defaults, options) ;
+
+ this._defaults = defaults;
+ this._name = pluginName;
+
+ this.init();
+ }
+
+ /**
+ * Handles an element stalking
+ */
+ Stalker.prototype.init = function()
+ {
+ this.jElement = $(this.element);
+
+ // save the element's original position and CSS
+ this._baseOffset = this.jElement.offset();
+ this._baseWidth = this.jElement.width();
+
+ // we need a placeholder to keep the document from reflowing
+ // use a clone to keep styles (esp. those related to width) but remove
+ // children to reduce id conflicts
+ this.placeholder = this.jElement.clone(false).empty().css('height', this.jElement.outerHeight());
+
+ this.stalking = false;
+
+ var me = this;
+
+ /**
+ * Starts an element stalking; applies custom styles and handles positioning
+ */
+ function setPosition(edge)
+ {
+ me.stalking = true;
+
+ var initial = {position: 'fixed'}, ending = $.extend({}, initial);
+ initial[edge] = -(me.jElement.outerHeight()) + 'px';
+ ending[edge] = parseInt(me.options.offset) + 'px';
+
+ var handler = function()
+ {
+ // give the element custom style while stalking; by default,
+ // force the element to have its original width and appear on top
+ var basicStalkerCSS = {width: me._baseWidth + 'px', 'z-index': stalkerZIndex};
+ if (typeof me.options.stalkerStyle == 'object')
+ {
+ me.jElement.css($.extend(basicStalkerCSS, me.options.stalkerStyle));
+ }
+ else
+ {
+ me.jElement.css(basicStalkerCSS).addClass(me.options.stalkerStyle);
+ }
+
+ if (me.options.animate)
+ {
+ me.jElement.before(me.placeholder).css(initial).animate(ending, 200);
+ }
+ else
+ {
+ me.jElement.before(me.placeholder).css(ending);
+ }
+ };
+
+ if (me.options.delay)
+ {
+ setTimeout(handler, me.options.delay);
+ }
+ else
+ {
+ handler();
+ }
+ }
+
+ /**
+ * Restores an element to its original state after stalking
+ * by refreshing it with its clone
+ */
+ function restoreOriginalState()
+ {
+ // discard the stalker and all its weird inline styles
+ me.jElement.detach();
+
+ // rip the guts out of the original and dump them into the clone
+ var contents = me.jElement.contents();
+ me._jElementClone.empty().append(contents);
+
+ me.placeholder.replaceWith(me._jElementClone);
+
+ // make the old clone the element we're tracking
+ me.jElement = me._jElementClone;
+
+ // create a new clone later, when we start stalking again
+
+ me.stalking = false;
+
+ if (me.options.stopCallback)
+ {
+ me.options.stopCallback.call(me.jElement[0]);
+ }
+ }
+
+ /**
+ * Performs the necessary checks of element position relative to
+ * the window, and causes the element to start or stop stalking
+ * accordingly
+ */
+ function stalk()
+ {
+ var pageTop = $(document).scrollTop();
+ var viewportHeight = $(window).height();
+ var pageBottom = pageTop + viewportHeight;
+
+ if (me.options.direction == 'down')
+ {
+ if (me._baseOffset.top < pageTop)
+ {
+ if (!me.stalking)
+ {
+ // create a clone of the element, which will be used to keep the
+ // element's original styles intact for when we're done stalking
+ // We want to do this as late as possible.
+ // We won't need the descendents, so don't bother with them
+ me._jElementClone = me.jElement.clone(true, false);
+
+ setPosition('top');
+
+ if (me.options.startCallback)
+ {
+ me.options.startCallback.call(me.jElement[0]);
+ }
+ }
+ }
+ else if (me.stalking)
+ {
+ restoreOriginalState();
+ }
+ }
+ else
+ {
+ if (me._baseOffset.top + me.jElement.outerHeight() > pageBottom)
+ {
+ if (!me.stalking)
+ {
+ // create a clone of the element, which will be used to keep the
+ // element's original styles intact for when we're done stalking
+ // We want to do this as late as possible.
+ // We won't need the descendents, so don't bother with them
+ me._jElementClone = me.jElement.clone(true, false);
+
+ setPosition('bottom');
+
+ if (me.options.startCallback)
+ {
+ me.options.startCallback.call(me.jElement[0]);
+ }
+ }
+ }
+ else if (me.stalking)
+ {
+ restoreOriginalState();
+ }
+
+ }
+ }
+
+ function handleEvent()
+ {
+ // since resize gets called when window zooms, re-cache element width
+ if (me.stalking)
+ {
+ me._baseWidth = me.placeholder.width();
+ me.jElement.width(me._baseWidth);
+ }
+ else
+ {
+ me._baseWidth = me.jElement.width();
+ }
+ stalk();
+ }
+
+ // set up event handlers and call immediately
+ $(window).on('scroll.stalker', handleEvent).on('resize.stalker', handleEvent);
+
+ stalk();
+ };
+
+ // A really lightweight plugin wrapper around the constructor,
+ // preventing against multiple instantiations
+ $.fn[pluginName] = function ( options )
+ {
+ return this.each(function ()
+ {
+ if (!$.data(this, 'plugin_' + pluginName))
+ {
+ $.data(this, 'plugin_' + pluginName, new Stalker( this, options ));
+ }
+ });
+ };
+
+}(jQuery, window));
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