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Event handling with PrototypeJS

I've talked about the basics of PrototypeJS a bit before so I hope you're convinced about the awesomeness of Prototype.

Now I want to talk a little more about how Prototype can make event handling easier.

You're probably used to handling Javascript events by defining a function and then specifying the different event calls inline. This can get hard to keep track of over time. You have to remember to add the function call in every time you add a form element. It can also cause trouble if you have to change the call for the event because you have to go and change it everywhere.

<head>                function checkboxClick(elem) {                  alert(elem.value);              }  </head><body></body>

Now here's the Prototype way

<head>      $$('input[type="checkbox"]').each( function(elem) {      Event.observe(elem, 'click', function(event) {        alert(this.value);      });    });  </head><body></body>

The functionality here is exactly the same as the first example but we've taken the important step of removing the Javascript code from the HTML. This makes it easier to change the functionality of click event as well as making it easier to handle changes to the HTML.

Here's a practical example. Let's say we'd like an easy way to have some links popup in new windows while other links open in the same window.

In this example, we're going to set it up so that every link with a class of offsite will popup in a new window.

<head>            $$('a.offsite').each( function(elem) {            Event.observe(elem, 'click', function(event) {      , 'offsitewindow');                Event.stop(event);            });        });    </head><body>    Onsite Link    Offsite Link 1    Offsite Link 2    Offsite Link 3</body>

We use the $$ to get all a tags with a class of offsite. Then we define a click event handler for each link which pops up a new window.

There's one new thing here to be aware of:


This stops the default action of the event. In this case, without it, clicking on the link would popup in a new window and in the current window.