Seeing at the function body, there buble up two obvious problems
function nextSlide(){
$('.slide').eq(0).fadeIn(fadeSpeed);
event.preventDefault();
}
You didn't pass event
, therefore when invoking this function, JS assumes that event
comes from global scope. Second, you'd usually want to prevent default action before starting doing anything, like this:
function nextSlide(event) {
event.preventDefault(); // <- That should come first
$('.slide').eq(0).fadeIn(fadeSpeed);
}
And lastly, it doesn't make too much sense to use inline JavaScript when you have already included jquery.
So, I'd rewrite your thing as:
$("img.nextSlide").click(function(event){
event.preventDefault();
$('.slide').eq(0).fadeIn(fadeSpeed);
});
$("img.prevSlide").click(function(event){
event.preventDefault();
$('.slide').eq(0).fadeOut(fadeSpeed);
});