Get the browser window's current scroll position in JavaScript.

"use strict";

/**
 * Get scroll position
 *
 * Use pageXOffset and pageYOffset if they are defined, otherwise scrollLeft and
 * scrollTop. You can omit el to use a default value of window.
 *
 * @example
 * getScrollPos() -> {x: 0, y: 200}
 *
 * @return {Object} An object containing the scroll position
 */
var getScrollPos = function getScrollPos() {
    var el = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : window;
    return {
        x: el.pageXOffset !== undefined ? el.pageXOffset : el.scrollLeft,
        y: el.pageYOffset !== undefined ? el.pageYOffset : el.scrollTop
    };
};

//
// es6 version
const getScrollPos = (el = window) => ({
    x: el.pageXOffset !== undefined ? el.pageXOffset : el.scrollLeft,
    y: el.pageYOffset !== undefined ? el.pageYOffset : el.scrollTop
});