获取滚动条默认的宽度

        var oo = document.createElement('div');
        var ii = document.createElement('div');
        ii.style.height = '1px';
        oo.appendChild(ii);
        oo.style.visibility = 'hidden';

        document.body.appendChild(oo);
        var wL = ii.clientWidth;
        var scrollbarWidth;
        oo.style.overflowY = 'scroll';

        scrollbarWidth = wL - ii.clientWidth;

        console.log('scrollbar  ' + scrollbarWidth);