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Introduction to Developing Web Applications with AJAX – Part 2
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Introduction to Developing Web Applications with AJAX – Part 2 [pri… http://www.regdeveloper.co.uk/2006/06/20/ajax_web_tutorial_part2/pr… 1 sur 8 29/06/2006 11:58 Reg Developer » Product Focus » Hands On Original URL: http://www.regdeveloper.co.uk/2006/06/20/ajax_web_tutorial_part2/ Introduction to Developing Web Applications with AJAX – Part 2 By Deepak Vohra Published Tuesday 20th June 2006 12:45 GMT Tutorial Suppose you fill out a form that requires a unique field value, for example a userid in a registration form. Ordinarily, you would specify a userid value and the other field values and submit the form with the Submit button. If the userid is not already taken you would be able to register, but if the userid is taken you would get a message that the user id value is invalid and you would have to fill out and resubmit the entire form. With the AJAX web technique the userid value may be validated at the time the value is specified in the input form, thus avoiding any need to resubmit the form. SPONSORED LINKS Rackspace, The Managed Hosting Specialist – its all we do! – Click here to find out more IT gurus seek Your counsel – Jobsite, The best people for the job You inspire awe – Jobsite, The best people for the job I-NET+ CERTIFICATION from the Register’s training library In the previous AJAX tutorial ( http://www.regdeveloper.co.uk/2006/06/09/ajax_web_tutorial/ ), we introduced the AJAX technology and performed the preliminary setup for a sample AJAX application. Now, we shall run the AJAX application we configured in the previous article. The example AJAX application validates data input in an HTML form. The input form requires a unique CatalogId to create a catalogue entry, so the input CatalogId in the form is validated against the database content to see if it is already specified. Note that data added to the HTML form are sent to the server as the data is added (not when the form is completed) and an HTTP servlet “immediately” returns an XML response that contains information about the validity of the input data. In the client application, the XMLHttpRequest response from the server is processed and if the instructions indicate that the data input is valid, a message “Catalog Id is Valid” is displayed. An XMLHttpRequest is sent to the server and a response received with each modification in the input field. The procedure to send an XMLHttpRequest request involves the following procedure: Invoke a JavaScript function from an HTML event. 1. Create an XMLHttpRequest object in the Jav