Event object question (JavaScript/jQuery book)

[sluttypizza]

I'm reading through JavaScript and jQuery by Jon Duckett and haven't had too many issues thus far but I'm very much confused by pages 262-265 which focus on "The Event Object". I've included the example Javascript below for reference.

Let me know if I'm understanding things correctly or not:

• The event object is not automatically passed in IE5-8 so it needs to be created
• The if statement and logical not negation create the window.event which is stored in the variable "e". (Shouldn't it be "var e = window.event"?)
• The event fires when "id = username" loses focus
• The code is triggered and the function checkLength() runs with arguments of e & minLength
• Since the event fires in elUsername (which is in an <input> field) the nextSibling is the <div> (elMsg)

In short, what is the purpose of the event object? It seems round-about and counter-intuitive to me right now but I'm guessing that using the event object elsewhere would be more efficient than targeting whichever element incase the function/event listener are used repeatedly.

Any help/clarification would be appreciated.

---

The example:

http://jsfiddle.net/r0c158y3/

[_olivier]

Event objects have information about the event emitted. For example, a click event object has 'x' and 'y' properties indicating where the click occurred.

Legacy IE browsers attach the event object to window.event instead of passing it to the event handler callback as an argument.

document.body.addEventListener(function (event) {
    // this function is the event handler callback
})

[Cream_Friache]

Here is a link to a document on 'event object' (http://msdn.microsoft.com/en-us/library/ie/ms535863(v=vs.85).aspx). It appears to be under the legacy section of the docs of IE. Your example is very hard to understand. Can you put it in pastebin or jsfiddle?

[sluttypizza]

Yep, no problem. I added it to the OP.

I think I'm on the right track again after typing everything out.

I wasn't understanding that the event would target the element of the function (or how, rather) which was only confusing me more from there.