Adding a custom JavaScript validation function callback

In this recipe, we will look at how we can validate the contents of a text box manually using JavaScript. This gives us complete flexibility by allowing us to use any tool available to us within JavaScript to validate the input. For example, we could perform validation based on today's date, or even look up allowed values against an external web service.

Getting ready

Please refer to the first recipe in this chapter for details on how to prepare a QuickForm web form which is the basis of this recipe.

How to do it...

Add the following code to our form definition in validation_form.php, just after the field definition:

$mform->addElement('text', 'mytext13', 'Custom');
$mform->addRule('mytext13', 'Custom', 'callback', 'mycallback', 'client');

We specified a custom validation function mycallback.

In our example, we must edit validation.php to include a JavaScript file that includes our callback function:

$PAGE->requires->js('/cook...