is event a global variable that is accessible ever

问题:

I was just playing around with event listeners with DOM and javascript and did notice this:

function chained(msg) {
    console.log(msg, event);
}

function onClick() {
    chained('the body was clicked');
}

document.body.addEventListener('click', onClick);

Now the funny thing...this will output:

"the body was clicked, (MouseEvent)"

Then I ask, why? how does it passes the event object without sending it on the chained call?

function chained(msg) {
    console.log(msg, namedEventObj); //throw error namedEventObj is not defined
}

function onClick(namedEventObj) {
    console.log(event); //outputs (MouseEvent);
    console.log(nameEventObj); //outputs (MouseEvent);
    chained('the body was clicked');
}

document.body.addEventListener('click', onClick);

Even If I declare the event obj to be passed on the onClick function as namedEventObj it will available only to onClick but not to chained function...I got this and this makes sense for me...but definitely not the event variable to be available to the chained function.

Anyone know why does it behaves like this?

The only thing I can think of is that event is in fact window.event and it makes itself available when some event dispatches and Event...but that would mean that any element could get that event information if called at the same time as the event when it triggers?

I am using Chrome 11.0.x

回答1:

One can access the current event through window.event. Just using event is implicitly accessing window.event.