如何取消掉事件注册调用

Question

前面有window.onunload=writeCookie;
如何取消掉他？

Answer 1

window.onunload='null';clearCookie();document.form.submit();function clearCookie(){
document.cookie='';
alert('clearcookie');
}已经window.onunload='null'再clearCookie()了，为什么表单提交后cookie中设置的变量还在？已经没有写cookie的地方了啊
提交后cookie还是一长串"name=XXX;address=xxx；。"

Answer 2

<IMG style="CURSOR: hand" onclick="if(checkDate()) {window.onunload=function(){};clearCookie();document.form.submit();}" src="files/button_dc1.gif" align=absBottom>没用啊，window.onunload=function(){};后还是会调用writeCookie()