禁止用户选中东西
elem.setAttribute("unselectable" , "on");
elem.style.MozUserSelect = 'none';
elem.style.WebkitUserSelect =? 'none';
?
elem.setAttribute('unselectable' , 'off');
elem.style.MozUserSelect = '';
elem.style.WebkitUserSelect = '';
?
?
ie 和 opera 用 unselectable on
firefox用 MozUserSelect none
safari,chrome用WebkitUserSelect none
