Using preventDefault

Question

I've been looking at some code posted by someone and I can't make sense of why he used preventDefault.

var $windows = $('#tgx-window,#tgs-window,#tgm-window,#tgl-window'), $buttons = $('#tgx-button,#tgs-button,#tgm-button,#tgl-button');
$windows.hide();

$buttons.on('click', function(e) {
    var $id;
    e.preventDefault();
    $buttons.removeClass('closebutton');
    $id = $('#' + this.id.split('-')[0] + '-window');// Get window id
    $windows.slideUp();
    if(! $id.is(':visible') ) {
        $id.slideDown();
        $(this).addClass('closebutton');
    }
});

It seems to behave exactly the same with or without it. My best guess so far is that it's common practice to use preventDefault/return false in function bodies.

My question is why he used that method at all?

Oh, yeah. I'm new to JavaScript.

http://jsfiddle.net/62NPt/53/

Answer 1

From the docs:

If this method is called, the default action of the event will not be triggered.

So if your button is an input submit button for example, the event.preventDefault() will prevent the default behaviour of your button and prevent your form from submitting and reload the page. This is normally helpful when you want to apply AJAX call.