/** 
 * @projectDescription Monitor Font Size Changes with jQuery 
 * 
 * @version 1.0 
 * @author Dave Cardwell 
 * 
 * jQuery-Em - $Revision$ ($Date$) 
 * http://davecardwell.co.uk/javascript/jquery/plugins/jquery-em/ 
 * 
 * Copyright ©2007 Dave Cardwell <http://davecardwell.co.uk/> 
 * 
 * Released under the MIT licence: 
 * http://www.opensource.org/licenses/mit-license.php 
 */ 
 
// Upon $(document).ready()… 
jQuery(function($) { 
    // Configuration… 
    var eventName = 'emchange'; 
     
     
    // Set up default options. 
    $.em = $.extend({ 
        /** 
         * The jQuery-Em version string. 
         * 
         * @example $.em.version; 
         * @desc '1.0a' 
         * 
         * @property 
         * @name version 
         * @type String 
         * @cat Plugins/Em 
         */ 
        version: '1.0', 
         
        /** 
         * The number of milliseconds to wait when polling for changes to the 
         * font size. 
         * 
         * @example $.em.delay = 400; 
         * @desc Defaults to 200. 
         * 
         * @property 
         * @name delay 
         * @type Number 
         * @cat Plugins/Em 
         */ 
        delay: 200, 
         
        /** 
         * The element used to detect changes to the font size. 
         * 
         * @example $.em.element = $('<div />')[0]; 
         * @desc Default is an empty, absolutely positioned, 100em-wide <div>. 
         * 
         * @private 
         * @property 
         * @name element 
         * @type Element 
         * @cat Plugins/Em 
         */ 
        element: $('<div />').css({ left:     '-100em', 
                                    position: 'absolute', 
                                    width:    '100em' }) 
                             .prependTo('body')[0], 
         
        /** 
         * The action to perform when a change in the font size is detected. 
         * 
         * @example $.em.action = function() { ... } 
         * @desc The default action is to trigger a global “emchange” event. 
         * You probably shouldn’t change this behaviour as other plugins may 
         * rely on it, but the option is here for completion. 
         * 
         * @example $(document).bind('emchange', function(e, cur, prev) {...}) 
         * @desc Any functions triggered on this event are passed the current 
         * font size, and last known font size as additional parameters. 
         * 
         * @private 
         * @property 
         * @name action 
         * @type Function 
         * @cat Plugins/Em 
         * @see current 
         * @see previous 
         */ 
        action: function() { 
            var currentWidth = $.em.element.offsetWidth / 100; 
             
            // If the font size has changed since we last checked… 
            if ( currentWidth != $.em.current ) { 
                /** 
                 * The previous pixel value of the user agent’s font size. See 
                 * $.em.current for caveats. Will initially be undefined until 
                 * the “emchange” event is triggered. 
                 * 
                 * @example $.em.previous; 
                 * @result 16 
                 * 
                 * @property 
                 * @name previous 
                 * @type Number 
                 * @cat Plugins/Em 
                 * @see current 
                 */ 
                $.em.previous = $.em.current; 
                 
                /** 
                 * The current pixel value of the user agent’s font size. As 
                 * with $.em.previous, this value *may* be subject to minor 
                 * browser rounding errors that mean you might not want to 
                 * rely upon it as an absolute value. 
                 * 
                 * @example $.em.current; 
                 * @result 14 
                 * 
                 * @property 
                 * @name current 
                 * @type Number 
                 * @cat Plugins/Em 
                 * @see previous 
                 */ 
                $.em.current = currentWidth; 
                 
                $.event.trigger(eventName, [$.em.current, $.em.previous]); 
            } 
        } 
    }, $.em ); 
     
     
    /** 
     * Bind a function to the emchange event of each matched element. 
     * 
     * @example $("p").emchange( function() { alert("Hello"); } ); 
     * 
     * @name emchange 
     * @type jQuery 
     * @param Function fn A function to bind to the emchange event. 
     * @cat Plugins/Em 
     */ 
 
    /** 
     * Trigger the emchange event of each matched element. 
     * 
     * @example $("p").emchange() 
     * 
     * @name emchange 
     * @type jQuery 
     * @cat Plugins/Em 
     */ 
    $.fn[eventName] = function(fn) { return fn ? this.bind(eventName, fn) 
                                               : this.trigger(eventName); }; 
     
     
    // Store the initial pixel value of the user agent’s font size. 
    $.em.current = $.em.element.offsetWidth / 100; 
     
    /** 
     * While polling for font-size changes, $.em.iid stores the intervalID in 
     * case you should want to cancel with clearInterval(). 
     * 
     * @example window.clearInterval( $.em.iid ); 
     *  
     * @property 
     * @name iid 
     * @type Number 
     * @cat Plugins/Em 
     */ 
    $.em.iid = setInterval( $.em.action, $.em.delay ); 
});