Popularity of jQuery:

JavaScript libraries usage statistics: jQuery is used on the 75% of the top 1 million web-sites.

jQuery(function($){ // document.ready and noConflict mode
	$('.target').css('background-color', 'yellow');
	$('.target').click(function() { // bind an event handler to the click 
		$(this).toggleClass('btn-primary');
		$('.log').append(' click-event');
	});
});