如何识别mouseEvent对象是来自onclick还是来自onmouseover？

Question

我有以下javascript代码：

document.body.onclick = fn
document.body.onmouseover = fn

function fn(mouseEvent) {
  ...
}

如何识别mouseEvent对象是来自onclick还是来自onmouseover？ mouseEvent是否在某处包含此信息？

ps：我知道我可以做这样的事情，但这是很多样板。

document.body.onclick = fnOnclick
document.body.onmouseover = fnOnMouseover

function fn(mouseEvent, source)
function fnOnclick(mouseEvent) { fn(mouseEvent, "onclick") }
function fnOnmouseover(mouseEvent) { fn(mouseEvent, "onmouseover ") }