if (!window.jasen.core.Position) {

        window.jasen.core.Position = {};

    }

    function Size(width, height) {

        this.width = parseFloat(width);

        this.height = parseFloat(height);

    }

    Size.prototype.toString = function () {

        return "width=" + this.width + ";height=" + this.height;

    }

    function Point(x, y) {

        this.x = parseFloat(x);

        this.y = parseFloat(y);

    }

    Point.prototype.toString = function () {

        return "x=" + this.x + ";y=" + this.y;

    }

    // 获取窗口的左上角的偏移量（相对屏幕）

    function getScreenOffset() {

        if (window.screenLeft) {

            return new Point(window.screenLeft, window.screenTop);

        }

        else if (window.screenX) { // Firefox

            return new Point(window.screenX, window.screenY);

        }

        return new Point(0, 0);

    }

    // 获取屏幕的大小

    function getScreenSize() {

        return new Size(window.screen.width, window.screen.height);

    }

    // 获取窗口中的文档显示区的大小

    function getVisibleSize() {

        if (window.innerWidth) {

            return new Size(window.innerWidth, window.innerHeight);

        }

        else if (document.documentElement && document.documentElement.clientWidth) {

            return new Size(document.documentElement.clientWidth, document.documentElement.clientHeight);

        }

        else if (document.body && document.body.clientWidth) {

            return new Size(document.body.clientWidth, document.body.clientHeight);

        }

        return new Size(0, 0);

    }

    // 获取窗口中的文档的偏移量（滚动条的值）

    function getPageOffset() {

        if (window.pageXOffset) {

            return new Point(window.pageXOffset, window.pageYOffset);

        }

        else if (document.documentElement && document.documentElement.scrollLeft) {

            return new Point(document.documentElement.scrollLeft, document.documentElement.scrollTop);

        }

        else if (document.body && document.body.scrollLeft) {

            return new Point(document.body.scrollLeft, document.body.scrollTop);

        }

        return new Point(0, 0);

    }

    var position = window.Position = window.jasen.core.Position;

    position.getScreenOffset = getScreenOffset;

    position.getScreenOffsetX = function () { return getScreenOffset().x; };

    position.getScreenOffsetY = function () { return getScreenOffset().y; };

    position.getScreenSize = getScreenSize;

    position.getScreenWidth = function () { return getScreenSize().width; };

    position.getScreenHeight = function () { return getScreenSize().height; };

    position.getVisibleSize = getVisibleSize;

    position.getVisibleWidth = function () { return getVisibleSize().width; };

    position.getVisibleHeight = function () { return getVisibleSize().height; };

    position.getPageOffset = getPageOffset;

    position.getPageOffsetX = function () { return getPageOffset().x; };

    position.getPageOffsetY = function () { return getPageOffset().y; };

    <script type="text/javascript">

        document.body.onclick = function () {

            alert(window.Position.getVisibleSize());

            alert(window.Position.getPageOffset());

        }

    </script>