Javascript 判断是否移动端

function isMobile() {
  var ua = navigator.userAgent;
  var ipad = ua.match(/(iPad).*OS\s([\d_]+)/),
  isIphone = !ipad && ua.match(/(iPhone\sOS)\s([\d_]+)/),
  isAndroid = ua.match(/(Android)\s+([\d.]+)/);
  return isIphone || isAndroid;
}