javascript判断是否按回车键并解决浏览器之间的差异

<li class="item pin">
<span class="overlabel" style="display: block;">请输入验证码</span>
<input type="text" class="txt" id="checkNum" name="checkNum" maxlength="4" onkeydown="keyboardEvent(event);" />
<img src="${basePath}/randomImageCodeStyle" width="60" height="28" id="chkNum" 　 title="单击重新加载验证码" style="cursor: hand" />
</li>

//监听Enter键自动提交事件
function keyboardEvent(event){
var keyCode=event.keyCode ? event.keyCode:event.which?event.which:event.charCode;//解决浏览器之间的差异问题
if(keyCode==13){
submitForm();
}
}