js中获取event keycode的兼容办法

window.onkeypress=function(e){
  var event = e || window.event, //在ff下event会做为参数传进来，ie下会在window下
  keyCode = event.which || event.keyCode，  //e.which是ff下获取keyCode的方式，ie下使用e.keyCode获取
  charCode = event.charCode;  
}