Skip to main content

How To Track Changes in the Location Hash

As the web becomes more "2.0" we're collapsing collections of pages into fewer and even single, more dynamic pages. Instead of ten pages of event listings, we might have page that loads further items dynamically as you scroll. The state that was once static to a page is now loose and can alter in the lifetime of a page, which grows longer every day. Parameters of the page state have always sat in either the path, in URLs like http://myblog.us/post/how-are-you or the querystring in cases like http://www.coolstore.com/view.html?product=4356.

Neither approach works when those parameters are changing for the life of the page, and where a single URL needs to be able to represent these multiple parameter values at any time. In most uses so far, the bullet is simply bitten. The user can browse to your site and click around, and if they bookmark or send the link to a friend, they'll always come back to the front page, because the state of the page is no longer held in that URL. This wasn't acceptable for long and a few projects, including GMail, have taken to tossing some state information into the hash or anchor of the URL, after the # symbol. This has traditionally told a browser to scroll to a <a> tag with that name, but if none exists it becomes, essentially, a no-op. We have a place in URL we can stare state, now, without causing page loads and persisting the state in links and bookmarks. There still haven't been great or standard ways to deal with this, yet.

A couple years ago I started my own attempt to make this easier, when I found existing libraries outdated or just not really doing what I hoped for. They either seemed to depend on obsolete versions of other libraries, or only give a little trigger when the hash changed. I thought we needed something more than that, because this is really replacing everything we used to use querystrings for. Sure, I could toss #2 or #43 at the end of the URL depending on what page of results you saw, but what if the state was more than a single number? Querystrings can store lots of variables. This is what I wanted within the hash.

Born was hashtrack.js!

The API is pretty simple. You can check and set variables in the hash with hashtrack.getVar() and hashtrack.setVar(). Changes to the hash or to specific variables in it can be registered with callbacks via hashtrack.onhashchange() and hashtrack.onhashvarchange(). You can view the full documentation, included embedded interactive examples, at the github pages hosting it.

Comments

schmichael said…
Thanks for the code! I've been using jQuery's History plugin, but it doesn't offer per-variable callbacks (and it seems to be unmaintained).

I removed the jQuery.each dependency in a fork on GitHub. I also fixed up the whitespace and tried to make jslint happy, but you can ignore those changesets if you want. :-)

@schmichael

Popular posts from this blog

CARDIAC: The Cardboard Computer

I am just so excited about this. CARDIAC. The Cardboard Computer. How cool is that? This piece of history is amazing and better than that: it is extremely accessible. This fantastic design was built in 1969 by David Hagelbarger at Bell Labs to explain what computers were to those who would otherwise have no exposure to them. Miraculously, the CARDIAC (CARDboard Interactive Aid to Computation) was able to actually function as a slow and rudimentary computer.  One of the most fascinating aspects of this gem is that at the time of its publication the scope it was able to demonstrate was actually useful in explaining what a computer was. Could you imagine trying to explain computers today with anything close to the CARDIAC? It had 100 memory locations and only ten instructions. The memory held signed 3-digit numbers (-999 through 999) and instructions could be encoded such that the first digit was the instruction and the second two digits were the address of memory to operate on

The Range of Content on Planet Python

I've gotten a number of requests lately to contribute only Python related material to the Planet Python feeds and to be honest these requests have both surprised and insulted me, but they've continued. I am pretty sure they've come from a very small number of people, but they have become consistent. This is probably because of my current habit of writing about NaNoWriMo every day and those who aren't interested not looking forward to having the rest of the month reading about my novel. Planet Python will be getting a feed of only relevant posts in the future, but I'm going to be honest: I am kind of upset about it. I don't care if anyone thinks it is unreasonable of me to be upset about it, because the truth is Planet Python means something to me. It was probably the first thing I did that I considered "being part of the community" when I submitted my meager RSS feed to be added some seven years ago. My blog and my name on the list of authors at Plan

Pythonic Defined

Introduction Losing is Good Strings Dictionaries Conclusion Introduction Veterans and novices alike of Python will hear the term "pythonic" thrown around, and even a number of the veterans don't know what it means. There are times I do not know what it means, but that doesn't mean I can define a pretty good idea of what "pythonic" really means. Now, it has been defined at times as being whatever the BDFL decides, but we'll pull that out of the picture. I want to talk about what the word means for us today, and how it applied to what we do in the real world. Languages have their strengths and their idioms (ways of doing things), and when you exploit those you embrace the heart of that language. You can often tell when a programmer writing in one language is actually more comfortable with another, because the code they right is telltale of the other language. Java developers are notorious for writing Java in every language they get their hands on. Ho