Part 1 – Description of the problem
Part 2 – this article (simple history replacement)
Part 3 – additional history items

As we saw earlier in part 1, hitting the back button into a page with filled in fields will not restore (all) the values, but merely the ones that exist at the time of the page loading. In some cases, for example cascading dropdowns, will not be shown or exist at all at the time of the page load.

What we will accomplish in this part is to push into the query string (without reloading the page!) the selected make and the selected model (where applicable).

We are going to make use of

history.replaceState(...)

function. There is a W3C standard available for this function (and others).  Note that this is supported on all browsers, but only the recent versions.

To do so we need a few things:

• A function to parse (a) query string; sadly JavaScript does not have anything built in, not even jQuery is of much help..
• Change the URL upon changing of selection
• Restore selection from the URL – including cascading

Great! Let’s start.

Upon a bit of searching around which turned into stackoverflowing, I reached the most voted question on this matter called ‘How can I get query string values in JavaScript?‘.

I really looked for a quick-simple-and-standards-compliant-and-so-on solution but the best I could scavenge was this:

function getParameterByName(name, url) {
    if (!url) url = window.location.href;
    name = name.replace(/[\[\]]/g, "\\$&");
    var regex = new RegExp("[?&]" + name + "(=([^&#]*)|&|#|$)"),
        results = regex.exec(url);
    if (!results) return null;
    if (!results[2]) return '';
    return decodeURIComponent(results[2].replace(/\+/g, " "));
}

Ugly but it works.

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Part 1 – this article
Part 2 – simple history replacement
Part 3 – additional history items

Have you ever come across a web page with a few fields, let’s say cascading drop downs, you know like these:

… and after carefully filling in the fields you submit, and you are taken to the next page. Only to find out that you made a mistake and you push the back button in your browser. Guess what, now (almost) all your fields are reset and you have to begin all over again. Frustrating.

Apart from that, I have noticed that “infinite scrolling” has really taken off in a lot of sites, some news site (for example this one – at least at the time of the writing) even change the URL as you scroll down into the next article.

And then I wondered, how could I use this gimmick into solving the first issue (i.e. losing fields information after pressing back) and I came up with two possible solutions to this. I will showcase a small PoC for each one in the next two parts.

First let’s consider the following minimal web project (ASP.NET MVC but since this is about JavaScript, the back end doesn’t really matter) with two drop-downs. The first dropdown will let you choose a make of automobiles and the second one will let you choose a model from that particular make. In the end you press continue and you are directed to a new page:

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