Tip of the Day

Tip of the Day: Calculating durations with Moment

Moment has quite a nice fluent interface for some operations, others just need a little more thought.

For example, I wanted the duration of something and I had recorded the start and end time. I thought something like this, finding the difference between two dates and converting it to a duration, would work:

var duration = endTime.diff(startTime).duration().asSeconds();

However, that doesn’t work.

What you have to do is find the difference, then pass that into the duration function, like this:

var duration = moment.duration(endTime.diff(startTime)).asSeconds();

And now I get what I wanted.

Software Development

Working with Modules in node.js

In my last post on node.js I showed how to set up a development environment to work with node. Now, I’m going to introduce some bits and pieces to get going a bit further than a simple hello world.


First off, unless you want to be working with JavaScript files that are thousands of lines long you’ll want to modularise your code into smaller components that you can bring in to other JavaScript files as required. From the API Documentation: “Node has a simple module loading system. In Node, files and modules are in one-to-one correspondence.”

The “require” keyword allows you to do this. You must also remember that require will return an object that represents that module, so you need to assign it to a variable.

Here is an example, showing you how to require the readline module so that you can ask questions at the command line.

var readline = require("readline"),
    rlInterface = readline.createInterface({
        input: process.stdin, 

rlInterface.question("What is your name? ", function(answer){
    console.log("Hello, "+answer+".");

And if you run the application, it will look something like this:

$ node whatsYourName.js
What is your name? Colin
Hello, Colin.


The above is great if you want to include a node module. But if you are building your own, then there is a little more work needing done.

In your module you need to add module.exports to indicate what is being exported from the module. Since it is just a bag of properties you can create what ever you need for the module.

e.g. This is the code for myModule.js

module.exports.someValue = "This is some value being exported from the module";
module.exports.someFunction = function(a, b){
    return a+b;

And the consumer of that module (moduleConsumer.js):

var myModule = require("./myModule.js");
console.log("This is someValue: "+myModule.someValue)
console.log("This is the result of someFunction: ", myModule.someFunction(2,3));

Which produces the output:

$ node moduleConsumer.js
This is someValue: This is some value being exported from the module
This is the result of someFunction:  5

One thing you might notice that is different from before is that when you require code that is in your project then you need to specify the path to the JavaScript file, even if it is in the same folder. So for files in the same folder you need to prefix the name of the JavaScript file with “./“.

If you have various files that need to include a specific module, then the first call to require will create the module, then each call after that will get a cached version of the module. So, if you put in a log statement at the top of your module to say that it is being loaded, then that log statement will only be run once regardless of the number of times you require that module.

Requiring a folder

You can require a folder rather than a specific file. In this case, what node does it looks for a file in the folder called packages.json, then index.js.

packages.json is a file containing a piece of json that describes module that bootstraps the rest. e.g.

{ "name" : "my-library",
  "main" : "./lib/my-library.js" }

The “main” property describes the JavaScript file that is the entry point into the module that bootstraps the rest.

If it finds an index.js file then that file is uses as the entry point that bootstraps the rest of the folder.

Software Development

Getting Started with AngularJS – The Application Module

As with all applications there has to be a starting point. Where does the application start? In AngularJS that starting point is the module.

And because a module is, well, modular, you can plug modules into each other to build the application, share components and so on.

Actually, I suppose in Angular it actually starts with a directive, that points to the module to start with, because, if you have more than one, which one do you start with?

<html ng-app="angularCatalogue">

The ng-app directive bootstraps the application by telling AngularJS which module contains the root of the application.

A module is defined like this:


The name of the above module is "angularCatalogue", the name of the application, which is what is placed in the ng-app directive in the html element previously.

You can also add as a second parameter to the module an array of other modules to inject. The modules don’t necessarily have to be loaded in any particular, so it is okay to refer to a module that may not exist at that point.

The module function returns a Module object, which you can then set up as you need it. Typically an application will have some sort of configuration, controllers, directives, services and so on.

Wiring up the view

In the html you will need to indicate where the view is to be placed.

You can do this via the ng-view directive, which can look like this:



<div ng-view></div>

Everything inside the element will be replaced with the contents of the view.

The application then needs to be told where the view is. You can configure the application module with that information, like this:

    .config(["$routeProvider", function($routeProvider){
                controller: "productSearchController"

The config call on the module allows the module to be configured. It takes an array that consisted of the names of objects to be injected into the configuration and the function that performs the configuration.

The function has a $routeProvider injected into it. This allows routing to be set up. In the example above a route is set up from the home page of the application ("/") that inserts the given template into the element (ng-view) that designated the view and it uses the given controller.

I’ll move onto controllers in an upcoming post.

A note on the dependency injection

If you never minify you javaScript you can get away with something like this:


You’ll notice that there is no array, it is just taking a function. Angular can work out from the parameter names what needs to be injected. However, if the code is minified most minifiers will alter the parameter names to save space in which case angular’s built in dependency injection framework fails because it no longer knows what to resolve things to. Minifiers do not, however, minify string literals. If the string literals exist then it will use them as to determine what gets resolved into which parameter position. The strings must match the position of their counterpart in the function parameters.

Therefore the minifier friendly version of the previous snippet becomes:

    .config(['$routeProvider', function($routeProvider){

A note on naming conventions

You can name things what you like but AngularJS has some conventions reserved for itself.

  • Its own services are prefixed with a $ (dollar). Never name your services with a dollar prefix as your code may become incompatible with future versions of angular.
  • Its own directives are prefixed with ng. Similarly to the previous convention, don’t name any of your directives with an ng prefix as it may clash with what’s in future versions of angular.
  • In javaScript everything is camel cased (the first word is all lower cased, subsequent words have the first letter capitalised), in the HTML dashes separate the words. So if you create a directive called myPersonalDirective when that directive is placed in HTML it becomes my-personal-directive.
CodeProject, Software Development

Automatically replacing an image on an HTML page when it is not found.

The project I’m working on has just moved the image hosting to Amazon S3. Previously what happened was that we had a big folder full of images that had been uploaded from our users and that if the site needed to render an image it would check the directory for the image it needed, if it didn’t have it, it would look for the original and then resize and render that (storing the resized version in the folder so it can be found the next time). If the original couldn’t be found either it displayed a replacement image in place that was basically an image that said “There is no image available.”

That worked well enough with a small number of users but it really didn’t scale well.

Now that we’ve moved the hosting to Amazon S3 we create all the image sizes needed at the time they are initially uploaded. If we need a new size we have a tool that will go and create all the resized versions for us. The only issue that remains is that some images don’t exist for various reasons. Much of the legacy data came from systems that were installed on people’s desktops and the image data simply never got sync’ed to the central server properly.

But there is a way around this on the browser. The img tag can have an onerror attribute applied, which can then call a function which replaces the image src with a dummy image that contains the message for when there is no image.

For example:

  <img src="error.jpg" onerror="replaceImage(this, 'replacement.jpg');" title="This image is replaced on an error"/>

<script type="text/javascript">
  function replaceImage(image, replacementUrl){

Although this looks a little ugly (putting in lots of onerror attributes on images) there is a lot less code to be written. When trying to achieve the same results in jQuery I eventually gave up. That’s not to say that it can’t be done, just that for pragmatic reasons I didn’t pursue it as I was spending too much time trying to get it to work.

The function does two things, first it removes the onerror because if the replacementUrl is also broken it will just recurse the call to the error handler and the browser will just slow right down. Second, it performs the actual replacement.

To see it in action there is an example page to demonstrate it.

I also tried to create a jQuery based solution to fit in with everything else. However, there were a couple of problems with a jQuery solution that were less than ideal.

  • You can’t attach an error event to the images because by the time you have done so the error event will be long past. You have to loop around all the images initially to find out which didn’t load before jQuery got a chance to get going.
  • For images that are added to the page by jQuery itself the .on does not work because delegated events, which allow you to create event handlers on elements before they are created, need the events to bubble up to a parent that did exist at the point the event handler was attached. The error event, among a small set of other events, does not bubble up. And if you attach it directly to the newly created element on the page then it will likely be too late, especially on a fast connection, as it will have already fired off the error event. You could do the same as before and check manually to see if the image loaded or not – but then the code is getting rather unwieldy and unmanageable.

In the end I found that the small bit of code that is called from the onerror attribute on each img element that needed it was more compact and didn’t require lots of extra lines of code to ensure that all the errors were corrected in the case that jQuery just didn’t get there in time.

Finally, if anyone has a solution in jQuery that does not require cluttering up the HTML, I’d like to see it

CodeProject, Software Development

Quick guide to Geolocation in Javascript

In some modern browsers, such as Chrome and Firefox you can access the geolocation of the device. That is, where the device is physically located.

The main function for achieving this is getCurrentPosition, which doesn’t return a position as you might expect. Rather, it takes a callback (and optionally a second if you want to handle error conditions).

I’ve put together a small example page showing this, which I’ll now walk through.

In the example, when the user clicks on the button on the page it will attempt to get the physical location of the device. This may or may not work for several reasons. If it doesn’t work then the browser may not support it, or the user may refuse to give permission to the site, or the geolocation service may not be working.

This first bit of code checks to see if the browser supports the geolocation API and if it does calls the function to get the location passing in the callbacks for success and error handling.

if (navigator.geolocation) {
    navigator.geolocation.getCurrentPosition(successCallback, errorCallback);
} else {
    displayErrorMessage("The browser does not support the Geolocation API.");

In this small example, the successCallback simply fills various spans with the results in the position and creates a URL that links to google maps to display a pin at the coordinates.

function successCallback(position) {
    $("#displayMap").attr("href", "http://maps.google.com/?q=" + position.coords.latitude + "," + position.coords.longitude);

The position has a timestamp and a set of coordinates. Since the geolocation may be cached the timestamp will give you an indication of how old the geolocation is.

The coords gives you various bits of information about the geolocation. The three values that will always be available are latitude, longitude and accuracy. The other values (such as altitude, heading and speed) may be nullable. The accuracy is in meters and can be used to gauge how good the lat/long is. The Lat/Long is in WGS84 decimal degrees.

In the event of an error, the errorCallback will receive some indication about what went wrong. The most common may be that the permission was denied, but other potential errors exist.

function errorCallback(error) {
    switch (error.code) {
        case error.PERMISSION_DENIED:
            displayErrorMessage("The request was denied. If a message seeking persmission was not displayed then check your browser settings.");
        case error.POSITION_UNAVAILABLE:
            displayErrorMessage("The position of the device could not be determined. For instance, one or more of the location providers used in the location acquisition process reported an internal error that caused the process to fail entirely.");
        case error.TIMEOUT:
            displayErrorMessage("The request to get user location timed out before the operation could complete.");
        case error.UNKNOWN_ERROR:
            displayErrorMessage("Something unexpected happened.");


How your browser reacts to requests for geolocation

Your browser may give you some form of alert to indicate that the site is requesting the geolocation. Chrome, for example, displays a bar just under the omnibox

Chome asks if it is okay to use geolocation

If a site has permission to get the geolocation then the icon above will be displayed in the omnibox to the right of the URL. If not, the icon will have a red cross over it. You can click this icon to change the settings at any time.


Finally, if you want to read the spec in full, it is available here: http://www.w3.org/TR/geolocation-API/



I keep hearing about friends using The Pomodoro Technique and I’ve decided I really need to just try it out for myself. I’m not yet sure if it will work for me, but I’ve been hearing positive things about it.

To that end I set myself the task of a small project using it, that is to create a web page with a pomodoro timer with a visible indicator of time left and that makes a noise when the timer expires. The final pomodoro is to write up this blog post.

This task has a mix of things I already know about (putting together a web page with HTML, CSS, JavaScript and jQuery) and things I would have to look up (like how to get a web page to emit a sound at a given point, have it respond to events at timed intervals, and deploy it to the web via Amazon’s AWS).

What I found was that 25 minutes actually goes past very quickly. Secondly, and this is more because it is the Christmas holidays, I still need to discipline myself not to jump to Facebook or Twitter each time my phone beeps or chirrups a notification at me. Similarly, in work I would probably have to discipline myself not to jump to Outlook or Skype when they pop up notifications.

On the whole, it looks like it could be fairly advantageous and I’ll continue to see if it helps productivity.

For the moment, if you do want to have a look at the very simple pomodoro timer that I created, then you can access it here: http://pomodoro.colinmackay.co.uk – I’m also happy to take suggestions on improvements if you think it could be made better.

Software Development

Developer Tools in IE Hides Bug

The other day I put some code on our UAT (User Acceptance Testing) server so that some new code could be tested and I started received a very alarming bug that one of the pages simply didn’t work at all. The page was in an administration section of the website and relied heavily on JavaScript even just to display the initial content (which was retrieved via an AJAX request)

As a quick initial smoke test I loaded the page up on my machine and it was working using my developer build. Then I looked at the page on the UAT server in case it was some quirk of the build and it was also working. I then noticed that the person doing the tests was running IE, so I though it might be a browser issue, so I loaded the page from the UAT server up again, this time using IE and it was still working on my machine.

Since it was lucky enough that the particular section was an admin section (which would be used only in-house) the people testing it were not actual customers of ours so I could walk over to their desk and ask for a demonstration in case there was some quirky step that had to be undertaken. When the page was loaded up I immediately saw that it didn’t work.

Being a developer my first instinct was to open up the Developer Tools in IE and have a look at what was happening. So I hit F12 and the reloaded the page…. and it started to work!  It worked with the Developer tools turned on!

I couldn’t fathom that out. What was so different about Internet Explorer when the Developer Tools were turned off so I started going through the various things that IE was showing me in the developer tools, stepping through code and watching the AJAX request go out then come back with data and start to process that data…. And then I noticed it. There was a line that said:

console.log("blah… blah…. blah…");

On a regular user’s machine the Developer Tools are never running, so it never has a console, so the JavaScript just broke.

Demonstrating the bug

How you you try this out? I’ve written a small demo to show what I mean. Obviously, you need to open it in Internet Explorer. I’ve tried it in IE 8.

If you have already opened the Developer Tools previously then you may find that they open automatically, which makes any testing impossible. Shutting them down and restarting IE doesn’t help. You have to go in to the registry and manually disable the developer tools.

To disable the Developer Tools in Internet Explorer you need to edit the system registry. Open up regedit and navigate to HKCU\Software\Microsoft\Internet Explorer\IEDevTools then create a DWORD called Disabled and give it the value of 1.

Once you have disabled the Developer Tools you’ll see that the page displays the text:

This paragraph has been update by javascript.

This paragraph is not yet updated by javascript, and if the Developer Tools are not present, it won’t update.

And a small warning triangle appears in the status bar of IE. Double clicking on the warning triangle brings up a dialog with some error information that looks like this:

To re-enable the Developer Tools simply delete that setting and restart Internet Explorer, press F12 to bring up the developer tools then open the demonstration page again.

Now the text displayed on the page reads:

This paragraph has been update by javascript.

This paragraph has also been updated by javascript, indicating the developer tools are present

Preventing this bug

Obviously running functions on the console object is not all that desirable in a production system so the idea is to remove all those calls so that IE won’t crash. If you find that is impractical you could put in some JavaScript before other JavaScript is run such as the following:

if (window.console === undefined) {
  console = {};
  console.log = function(){};

This will ensure that if a console object does not exist then one is created and a dummy function is attached to it. If you use other functions on the console object then you should add them also in a similar way.

The above demonstration has been updated to show this console “protection” in action.