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/** 
 * This function check an element is scrolled into view area on screen.
 * @param elem; use CSS Selector syntax to specific an element.
 * @return boolean;
 * @author Scott Dowding
 * @refer http://stackoverflow.com/questions/487073
 */
function isScrolledIntoView(elem)
{
    var $elem = $(elem);
    var $window = $(window);

    var docViewTop = $window.scrollTop();
    var docViewBottom = docViewTop + $window.height();

    var elemTop = $elem.offset().top;
    var elemBottom = elemTop + $elem.height();

    return ((elemBottom <= docViewBottom) && (elemTop >= docViewTop));
}

/**
 * Generate random string.
 * @param Integer len; Length of string
 * @return String;
 * @author Roger Knapp
 * @refer http://stackoverflow.com/a/1349426/1235074
 */
function random(len)
{
    var text = "";
    var possible = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";

    for( var i=0; i < len; i++ )
        text += possible.charAt(Math.floor(Math.random() * possible.length));

    return text;
}