Question

I’m working in PHP to build a form. I know how to display the form and then take submitted values from the $_POST variable, and I know how to validate those variables and display a “Thank You” or an “Error” page depending on the input.

What I don’t know how to do, though, is create a client-side-like system wherein despite having my users hit a “back” button a separate screen I can then take the information I gathered from the first submission and display dynamic error messages like “Please provide a valid email address” or “First name is a required field” next to the fields that were entered incorrectly. I’d also like to retrieve any previously submitted data that was valid and have it populate in the form so users don’t get frustrated by losing everything they entered.

What is the right approach to accomplishing something like this in PHP? I originally thought if I could pass back an array of error messages with an input type=”hidden” tag I could then pull my values and display messages dynamically with PHP, but I keep getting stuck in that approach.

Answer 1

You could add the errors a php session, but this creates issues for users who have multiple browser tabs open.

My preferred method is to have the form submit to the same page and put the errors directly on that page so the user does not have to click the back button. That way you can highlight the fields directly in the form (make the background or outline red or something similar.)

<input type="text" 
    <?php (empty($_POST['field']?'style="backgroung-color: red;"':''))?>
    name="field" value="<?php echo $_POST['field']?>" />

You can put <input type="text" name="field" value="<?php echo $_POST['field']?>" /> to get the old value.
Because the web is, by definition, stateless, there is no really good way to track what the user does when they hit the back button. There are hacks that work using a hidden iframe, but that is way more trouble that what you are looking for.