A simple JavaScript that lets you use your browser's back/forward buttons for in-page navigation by adding custom 'next' and 'previous' events to the window object.

history_navigation.js

/*
 * Lets you use your browser's back/forward buttons for in-page navigation by
 * adding custom 'next' and 'previous' events to the window object.
 *
 * Copyright (c) 2011 Tobias Schneider <[email protected]>
 * This script is freely distributable under the terms of the MIT license.
 *
 * Example:
 *
 *	window.addEventListener('next', function(){
 *		console.log('forward button clicked');
 *	}, false);
 *
 *	window.addEventListener('previous', function(){
 *		console.log('back button clicked');
 *	}, false);
 */

if(window.history && history.pushState){ // check for history api support
	window.addEventListener('load', function(){
		// create history states
		history.pushState(-1, null); // back state
		history.pushState(0, null); // main state
		history.pushState(1, null); // forward state
		history.go(-1); // start in main state
				
		this.addEventListener('popstate', function(event, state){
			// check history state and fire custom events
			if(state = event.state){
	
				event = document.createEvent('Event');
				event.initEvent(state > 0 ? 'next' : 'previous', true, true);
				this.dispatchEvent(event);
				
				// reset state
				history.go(-state);
			}
		}, false);
	}, false);
}

Line 20 should be using an evaluation === not an assignment =