A somewhat cross-browser implementation of getting the current `scrollTop` value of the body/document element.

document-scrolltop-shim.js

/**
 * document-scrolltop-shim.js
 * 
 * Cross-browser adjustments for getting and setting the current scrollTop -value for 
 * the body/html element.
 * 
 * @author Otto Rask
 */

/**
 * Get the scrollTop from either body or html element. As only one
 * or the other is used in a browser, it returns zero (correct),
 * or if either value is set to something else than 0 then the 
 * value.
 * 
 * @return int
 */
var getDocumentScrollTop = function () {
    return document.body.scrollTop || document.documentElement.scrollTop || 0;
};

/**
 * Set the scrollTop value. Setting to both should work as browsers
 * only use one or the other.
 *
 * @param int val
 */
var setDocumentScrollTop = function (val) {
    document.body.scrollTop = val;
    document.documentElement.scrollTop = val;
};