跨浏览器绑定事件

function addEventSamp(obj, evt, fn) {
  if (!oTarget) {
    return;
  }
  if (obj.addEventListener) {
    obj.addEventListener(evt, fn, false);
  } else if (obj.attachEvent) {
    obj.attachEvent("on" + evt, fn);
  } else {
    oTarget["on" + sEvtType] = fn;
  }
}