Learning PHP, MySQL, JavaScript, and CSS, 2nd Edition

signup.php

Now we need a module to enable users to join the new network: that’s Example 21-5, signup.php. This is a slightly longer program, but you’ve seen all its parts before.

Let’s start by looking at the end block of HTML. This is a simple form that allows a username and password to be entered. But note the use of the empty <span> given the id of 'info'. This will be the destination of the Ajax call in this program that checks whether a desired username is available. See Chapter 17 for a complete description of how this works.

Checking for Username Availability

Now go back to the program start, and you’ll see a block of JavaScript that starts with the function checkUser. This is called by the JavaScript onBlur event when focus is removed from the username field of the form. First it sets the contents of the <span> I mentioned (with the id of 'info') to an empty string, which clears it in case it previously had a value.

Next a request is made to the program checkuser.php, which reports whether the username user is available. The returned result of the Ajax call, a friendly message, is then placed in the 'info' span.

After the JavaScript section comes some PHP code that you should recognize from the discussion of form validation in Chapter 16. This section also uses the sanitizeString function to remove potentially malicious characters before looking up the username in the database and, if it’s not already taken, inserting the new username $user and password $pass.

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