wheresrhys

I’m always dismayed by the lack of debugging information out there. Yes, there is plenty of information on how to fix particular bugs, but very little on the more general heuristic processes for finding the source of a bug. This may be because debugging is, by its very nature, a thankless process of trial and error.

But nevertheless, I’ve just discovered for myself (though it may be common practice for others already) a technique for debugging when the bug lies within a function which runs numerous times without fail, but when fired on another particular occasion, fails. For example, you have one function which creates shopping basket items from all your user’s saved data at startup, but when you try and use the same function later to create another item based on user input, the function fails.

Putting some var_dump() [php] or console.log() [javascript] calls inside the function will result in reams of information being printed out, most of it useless as its produced by the successfully running first calls to the function. So what I now do is this:

Change

function myFunction(param1, param2, ..., paramN) {
    some = code;
    console.log(something);
    some = more(code);
}

to

myFunction(param1, param2, ..., paramN, test) {
    var some = code;
    if(test) {
        console.log(something);
    }
     some = more(code);
}

And change the function call that needs debugging from

myFunction(a, b, ... N)

to

myFunction(a, b, ... N, true)

Now you will only be shown the debugging messages when you need them. It’s particularly useful for javascript as the console area of firebug is so small so its good to limit messages to only those which are relevant.

In previous posts I’ve covered the inherent difficulty of geocoding addresses and postcodes in the UK, specifically in order use the geocodes with Google maps. I learned a lot about the limitations of Google’s various geocoding services. To sum up the situation:

• The Google maps API’s geocoding webservice is buggy: giving more address details can give a less accurate, and in many cases plain wrong, geocode. However, the GClientGeocoder class built into Google maps fares a lot better with addresses…
• … apart from when the address entered is a postcode. Then it geocodes to the central point of the postcode sector, rather than the precise postcode location, i.e if you search for E3 4GY or E3 4NT, it will return the geocode for the centre of E3 4 in both cases.
• But, as I discovered when trying an alternative route to postcode geocoding, the Google Ajax search API, the localSearch class in particular, gives very accurate geocodes for full postcodes.

Previously I’d been geocoding large batches of addresses/postcodes, but having got the geocodes in order to plot points on the map, I wanted to add search functionality to the map, so that it would zoom in on a given address/postcode. I wanted it to be accurate for both addresses and postcodes, so using what I’d learned, I wrote a javascript function, geocodeUKAddress, which always returns the best geocode that Google can offer, so your website can be as reliable as a London cabbie (again, I can’t embed it here as javascript has a habit of breaking wordpress, though there must be some way to make it safe – I will research).

You will need to include the following in ther head of your webpage too

<script src="http://maps.google.com/maps?file=api&amp;v=2&amp;key=your_api_key_here" type="text/javascript"></script>
<script src="http://www.google.com/jsapi" type="text/javascript"></script>

I can’t take credit for the regular expression that recognises UK postcodes, but apart from that, it’s all my own work, which anyone can feel free to use. Unless you maybe work for Rupert Murdoch.