Compatible handling of event objects under Firefox

I talked about the event object yesterday,

function calc(event){
var event=event||window.event
console.log(event);

}

The encapsulated function where the parameter event is abbreviated as follows

function calc(e){
var event=e||window.event
console.log(event);

}

will report an error

提示，event is not defined 

So the solution is, don't shorthand.