Using Ajax to look up e-mail addresses

We mentioned in a much earlier recipe that we would come back to an Ajax example later. There's a reason for that — it's not very difficult to add Ajax functionality to ChronoForms, but it's not the easiest task in the world either.

We'll walk through a fairly simple example here which will provide you with the basic experience to build more complex applications. You will need some knowledge of JavaScript to follow through this recipe.

Normally, the only communication between the ChronoForms client (the user in their browser) and the server (the website host) is when a page is loaded or a form is submitted. Form HTML is sent to the client and a $_POST array of results is returned. Ajax is a technique, or a group of techniques, that enables communication while the user is browsing the page without them having to submit the form.

As usual, at the browser end the Ajax communication is driven by JavaScript and at the server end we'll be responding using PHP...