Recently BVSTools went live with their mobile/responsive web site.  We decided at this time to set it up as a Single Page Application (SPA) style web site.

Because of this design, the back and forward buttons don't work traditionally like they would.  This is because each time a "link" is clicked instead of changing the location of the web browser to another web page, we simply replace the content on the main part of the page with the new information.

One day we got a call from a customer who said they loved the new site, but didn't like that the back button didn't work within the site.  I explained that yes, that's an issue with SPA web sites and that we were looking into a solution.

What we came up with was using the new HTML5 pushstate and popstate APIs that are available to manipulate history.  

Because we already had a JavaScript function that would "load" the contents of a link into the page, it was actually quite simple to do.  Our original function was as follows:

function loadBodyContent(path, callback) {

	$.get( path, function( data ) {
		$("#bodyContent").html( data );
		$("#bodyContent").append("<div id='footerContent'></div>");
		$("#footerContent").load("/ssi/footer.html");
		
		if (callback) callback();
	});
	
}

When we look at the loadBodyContent() function we see that we can pass in a path to load (and an optional callback function, which we're not worried about here).

The content from the path is loaded into the bodyContent div of the web  page, and then we tack on the footer portion of the page as well.

Now that we wish to manipulate the history to allow the Back and Forward buttons to work, we updated our function to this:

function loadBodyContent(path, addToHistory, callback) {
	
	$.get( path, function( data ) {
		$("#bodyContent").html( data );
		$("#bodyContent").append("<div id='footerContent'></div>");
		$("#footerContent").load("/ssi/footer.html");
		
		if (addToHistory != false) {
			addHistory(path);
		}
		
		if (callback) callback();
	});
	
}

We see that we have a new (and optional) parameter named addToHistory.  If this value is not false, we call the addHistory() function which looks like this:

function addHistory(path) {
	history.pushState(path, null, null);
}

What this is doing is pushing some information to the history stack.  Most sites will use the 3rd parameter (which is a URI parameter) but we found this also changes the URL in the web page and attempts to load... in our case we don't want that.  So, we used only the first parameter which can be retrieved when the back button is pressed.

Which leads us to the next step... how do we capture the Back or Forward buttons on a browser?  With a window event listener.  We added the following code to our main JavaScript file:

	window.addEventListener('popstate', function(e) {
		var location = e.state;
	
		if (location != null) {
			loadBodyContent(location,false);
			$('.addedMenuNavBarItem').remove();

		} else {
			window.history.back();
		}
	});

Now, when the Back or Forward buttons are pressed, we're able to get the last history item's value (the location).  We check if it's not null, and if it's not, we use it to call the loadBodyContent() function again, this time passing the boolean value of false so this location is not added to the history.

This works pretty slick on the browsers I've tested.  If you want to try things out feel free to visit our responsive site at http://m.bvstools.com.