I am new to JavaScript/jQuery and I've been learning how to make functions. A lot of functions have cropped up with (e) in brackets. Let me show you what I mean:
$(this).click(function(e) {
// does something
});
It always appears that the function doesn't even use the value of (e), so why is it there so often?
e是event对象的短var引用，它将被传递给事件处理程序.
事件对象本质上有很多有趣的方法和属性，可以在事件处理程序中使用.
In the example you have posted is a click handler which is a MouseEvent
$(<element selector>).click(function(e) {
// does something
alert(e.type); //will return you click
}
DEMO - Mouse Events DEMO uses e.which and e.type
Some useful references:
http://api.jquery.com/category/events/
http://www.quirksmode.org/js/events_properties.html
http://www.javascriptkit.com/jsref/event.shtml