Make that form for User friendly!

I am reading the jQuery Cookbook at the moment. I will blog some interesting examples that I am come across and pad them out - if even only slightly - in the hope that they make more sense to the untrained eye. Let's begin! Consider a form as such:

Who is going to win the Heineken cup next year?

• Leinster
• Munster
• Ulster
• Connacht
• Other

Click on any one of the teams, notice that the radio box is selected. Then start typing in the "Other" text box. Isn't it a bit odd that the team you previously selected is still selected even though you clearly started typing in the "Other" textbox? Does the user seriously have to explictly select the "other" radio button even though an "other" indication has already been given? Now, try this. Clear out the "other" text box and select another team. Then select the "other" radio button. Notice that the "other" textbox does not have focus even though you are hardly going to click the "other" check box and not want to type anything into the corresponding text field. Good GUI should assume the user will want to behave rationally. When the "Other" radio box is selected, it makes sense that its adjacent text box should get focus. Remember good usability means the user can achieve what they want with less clicking. And remember, good usability means that things are intuitive and GUIs do not display contradictions. So with all that in mind, we can include the discussed usability guidelines and come up with something like this:

Who is going to win the Heineken cup next year?

• Leinster
• Munster
• Ulster
• Connacht
• Other

So how did we do that? Well let's take a look at code:

Discussion:

1. :text is a JQuery psuedo class Selector which selects all elements of type text. As per JQuery recommendations, pseudo class Selectors should be preceded with another selector or tag element otherwise the universal selector is implied. In this case we do input:text and only one text box will be selected. That's ok.
2. The .each(function(){ means iterate overall inputs of type text and execute the specified function. Don't forget ".each" can operate on sets of elements of any size including just 1 which is the case in this example.
3. $(this) corresponds to the object which is being operated on by each. In this case it is each input text box. If you don't believe me add:

   
     console.log("this is: " + $(this)[0].id);
   
   

   and you will see something like:

   this is: Source5Txt in the console.

4. The inputText button and radio button are stored in the local context. This is for efficiency.

Til the next time take care of yourselves.

How JQuery changed events...

Event handling helps to enrich any application and that most definitely includes web applications. Do this when the button is clicked! Do this when the page has finished loading! Client side JavaScript has a range of event handling options. Before the days of funky JavaScript libraries such as JQuery, when the web was in its embryonic stage, event handling was achieved purely in JavaScript. One technique was to set the event handling properties to some JavaScript code. For example:

...

Here the onclick event property is set so that the an alert message is shown when the button is clicked. The Window object, Document node and the various Element objects all have a selection of event properties. Some of the more interesting ones are:

• window.unload - triggered when user is navigating away from from a document.
• form.onchange - can be used to capture a change from any element in the form thru a technique known as bubbling.
• element.onload - every document element (e.g. ,

All seemed much nicer, but IE complicated things:

1. IE8 did not support addEventListener(). Instead you had to use attachEvent()
2. Event handlers usually receive an Event object (http://www.w3schools.com/jsref/dom_obj_event.asp) which contains details of the event. This will contain properties such as the element that trigged the event, the name of the event and the time it was created etc. To receive this event simply add it to the event handler.

   button.addEventListener("click", function(event) {
       alert("You clicked me with an event of type!" + event.type)}, false);
   

   But you guessed it, IE8 did not support this mechanism to get details of the event and instead, you had to check the global variable window.event to get information about it. This lead to messy JavaScript code such as

   function handler(event) {
       event = event || window.event;  // got to cater for Microsoft!
   }
   

3. The "this" keyword in the event handling code usually referred to the document element that fired the event. However in IE8's attachEvent(), the this referred to the global window.

JQuery comes to the rescue providing APIs that work in all browsers. The commonly used events (e.g click, load) have their own event registration APIs (click(), load()). Similar to JavaScript's addEventListener() the JQuery event handler APIs allow multiple event handling logic to be associated with the same event. And similar to JavaScript, JQuery event handler functions do not have to have arguments or return values but both are supported. The value add being that JQuery APIs work and all browsers - that means event objects are passed into event handlers for poor old IE8!

//add to all button elements
$("button").click(function() {alert("You clicked me");}); .

So JQuery clearly solves some problems here. Does it offer anything else? Of course... the bind() API. This allows:

• the same handler to be executed for multiple events. Just separate the events by a space.

  // invoke myEventHanlder for any click, mousedown events for any div elements.
  $('div').bind('click mousedown', myEventHandler);  
  

• the same handler function to be reused with different data. This is achieved by passing an Object literal as the second object in the bind API. The object literal values can then be read in the event handler via the event objects data properties.

  // call buttonClicked and pass color red to it.
  jQuery('#button1').bind('click', {team:'Leinster'}, buttonClicked);
  // call the same buttonClicked function but pass blue. 
  jQuery('#button2').bind('click', {team:'Munster'}, buttonClicked); 
  

  buttonClicked function could then be something like:

  function buttonClicked(event) {
      alert("you selected team" + event.data.team);
  }
  

• Refer to multipe event handlers at the same time. This is achieved in JQuery by using namespaces for the events. Suppose you want to group a selection of events. You could put them all into the same namespace click.myclickevents.

  $("#myButton1").bind('click.myclickevents', myfunction());
  $("#myButton1").bind('mousedown.myclickevents', myfunction());
  

Because they are grouped they can be reffered to now at the same time. This comes in handy if you want to remove them.

$("#myButton1").unbind('myclickevents');

In addition JQuery provides:

• The one() API. This is similar to bind, except the eventhandlers only get called once. They are then deregistered.
• The trigger() API. This provides the ability to manually cause event handlers (including custom events) to be invoked.
• Live events This is like the event handling achieved with the bind() except it will also add event handling logic to new elements that are to still to be created, whereas bind() only adds it to existing elements.

The End?

Not quite. In order to stop people getting confused about the various JQuery event handling APIs JQuery unified them all into one API, the on() API. See also 1.7 release notes.

Are you leaving my site?

A website will always contain some links. Links fall into one of two categories:

1. Internal links - links to other parts of your website.
2. External links - links to other websites external to your website.

There are times when it might make sense to warn the user you are leaving your site. For example, you may have a SAAS style architecture with external links. It is good usability to differentiate links that keep the user on the site and links which will take the user away from the site especially if the latter could invalidate a transaction or session. Even if nothing could become invalidated it must just to differentiate in cases when the site the user will be trvalleing to next is very similar (which might lead the user to think it is the same site), or it might just be nice to say bye.

Well one way you could do this is to use some JQuery to select to all external links and add some JavaScript to execute to warn the user of the results of their action.

Check it out...

Try it out...

• www.google.com
• http://dublintech.blogspot.ie

An explanation of the code:

• a[href^='http:'

  The ^ after href means means all elements that begin exactly with http:. This is an example of how JQuery builds on CSS selectors.

• :not([href*='"+location.hostname+"'])

  means match elements that do not match the window.location.host property. Don't forget jquery provides many powerful selection filter expressions using the (:) syntax, Other examples are :first, :odd and :even.

• ... location.hostname

  is the dom way of figuring out the hostname of your site.

• attr("target","_blank")

  is a browser standard to open a new window.

• .click

  is the JQuery method whichs binds custom event handler to the the JavaScript "click" event.