Initial argument for the event listener

If I have event handlers registered inline in my markup (even though it's deprecated) like

 span id="..." onclick="foo(p1,p2,p3)"

how do I access the "event" object in the event handler function foo? Is changing the above to

 span id="..." onclick="foo(event,p1,p2,p3)"

and then using it in foo like:

function foo(e,p1,p2,p3)
{
   if (!e) e = window.event;
}

the correct way to do it? I couldn't find any documentation on this, so I'm hesitant to rely on it. Does the first parameter in an inline event handler always represent the event object when named as such in the onclick=... attribute? Is this behavior consistent across browsers or is it risky to use? And if the event object is not explicitly named, are the other parameters considered normal and the event object not passed?

What are your thoughts on this?

javascriptdom-events

Answer №1

Your interpretation of the code is incorrect.

The text you input into the inline handler functions as standard JavaScript code. It doesn't necessarily have to be a single function call; it can include multiple statements separated by semicolons.

The code within the inline handler will have access to a variable known as event, which represents the event object.

By using onclick="foo(event,p1,p2,p3)", you're executing a typical function call and passing the values of four variables named event, p1, p2, and p3 as arguments to the function.

Answer №2

Check out this source. It appears to match up with the example you provided. However, it's worth noting that it may not work the same way in Internet Explorer, so be sure to verify if the first argument (event object) is defined and if not, use window.event.

Here's another resource here. I find the Mozilla Developer Network to be quite useful.

Answer №3

After conducting some tests in Firefox (3.5.8/linux), I have discovered some interesting findings. I was surprised to learn about the usage of 'event' in Example 2, which actually works correctly in Firefox. However, it is not always the case that the first variable passed to a function is the event. It appears that 'event' is registered within a global object, but I have yet to identify which one it is. (Definitely not document or window!)

In the foo function, the line of code:

if (!e) e = window.event;

is necessary to handle events in Internet Explorer. This approach will work in both IE and Firefox. If you do not pass a variable named 'event', like in your second example, the parameters will be treated as normal parameters and the event object will not be passed.

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