cbpAnimatedHeader.js

/**
 * cbpAnimatedHeader.js v1.0.0
 * http://www.codrops.com
 *
 * Licensed under the MIT license.
 * http://www.opensource.org/licenses/mit-license.php
 *
 * Copyright 2013, Codrops
 * http://www.codrops.com
 */
var cbpAnimatedHeader = (function() {

	var docElem = document.documentElement,
		header = document.querySelector( '.cbp-af-header' ),
		didScroll = false,
		changeHeaderOn = 300;

	function init() {
		window.addEventListener( 'scroll', function( event ) {
			if( !didScroll ) {
				didScroll = true;
				setTimeout( scrollPage, 250 );
			}
		}, false );
	}

	function scrollPage() {
		var sy = scrollY();
		if ( sy >= changeHeaderOn ) {
			classie.add( header, 'cbp-af-header-shrink' );
		}
		else {
			classie.remove( header, 'cbp-af-header-shrink' );
		}
		didScroll = false;
	}

	function scrollY() {
		return window.pageYOffset || docElem.scrollTop;
	}

	init();

})();

var cbpAnimatedHeader = function(headerName, className) {

    var docElem = document.documentElement,
        header = document.querySelector( headerName ),
        didScroll = false,
        changeHeaderOn = 300;

    function init() {
        window.addEventListener( 'scroll', function( event ) {
            if( !didScroll ) {
                didScroll = true;
                setTimeout( scrollPage, 250 );
            }
        }, false );
    }

    function scrollPage() {
        var sy = scrollY();
        if ( sy >= changeHeaderOn ) {
            classie.add( header, className);
        }
        else {
            classie.remove( header, className);
        }
        didScroll = false;
    }

    function scrollY() {
        return window.pageYOffset || docElem.scrollTop;
    }

    init();

};

Other file:

cbpAnimatedHeader('.cbp-af-header', 'cbp-af-header-shrink' );