javascript caller 显示谁调用了我这个方法

<script type="text/javascript">
function whoCallMe(){
alert("my caller is"+whoCallMe.caller);//输出自己的Caller
}
function callerA(){
whoCallMe();
};
function calllerB(){
whoCallerMe();
};
window.onload=function(){
alert(whoCallMe.caller);
alert(whoCallMe()); 
callerA(); 
}
</script>