Simple function to pulsate element using jQuery animate.

pulsar.js

/**
 * pulsar
 * @description Will change the element's opacity in a recursing manner.
 * @param  {Object} elm     A DOM or jQuery element object
 * @param  {Object} options Options to override defaults, see var settings for those available
 * @return {Void}
 *
 * @see jQuery.animate http://api.jquery.com/animate/
 */
var pulsar = function( elm, options ) {
	// Set our defaults
	var settings = $.extend({
		prop_start: { opacity: 0.4 },
		prop_end:   { opacity: 1 },
		duration:   1000,
		easing:    'linear'
	}, options );

	// Animate that element
	$( elm ).animate( settings.prop_start, settings.duration, settings.easing, function(){
		$(this).animate( settings.prop_end, settings.duration, settings.easing, pulsar(this) );
	});
};