The toggle() method was deprecated in jQuery 1.8 and removed in 1.9.
In jQuery 1.9 the toggle() method does not toggle between two or more functions on a click event, it just toggles the visibility of an element.

Here is a quick way of replacing it:

var toggle = 0;
$('#toggle-btn').on('click', function(event) {
	event.preventDefault();
	if ( toggle == 1 ){
		// not clicked
		$(this).removeClass('clicked');
		toggle = 0;
	} else {
		// clicked
		$(this).addClass('clicked');
		toggle = 1;
	}
});

or just using a class,

$('#toggle-btn').on('click', function(event) {
	event.preventDefault();
	if ( $(this).hasClass('active') ) {
		$(this).removeClass('active');
	} else {
		$(this).addClass('active');
	}
});

See demo here.