Reading and printing user inputs in HTML in PHP

Question

I have got a form (php in html or the other way around). Once user selects an option in a drop down list, it would get the input value and create a few text boxes. It seems like I have to use onchange(). How do I read the input and perform logics within the script inself? Instead of opening another .php script?

Currently this is what I have.

<?php
$tables = $_POST["tables"];
?>

<html>
<body>

<form method="post" action="<?php echo $PHP_SELF;?>">
Table Name: <div id="tables">
<select name="tables">
<option value="Applications">Application</option>
<option value="Device">Device</option>
</select>
</div>
</form>

<?
echo "".$tables."";
?>

The onchange() event is JavaScript, not PHP. As @nickb said in his answer, PHP doesn't know anything has changed until the user submits the form. Also, it's never a good idea to use $PHP_SELF in a form like that, it opens you up to XSS attacks. I always just hard-code the page name (for example, if this page was named tables.php: <form action="tables.php" method="post">), it is a pain to have to update it when you rename a page but it's not that big a deal. — Useless Code
– Useless Code, Commented Jan 27, 2012 at 4:58

nickb · Accepted Answer · 2012-01-27 04:54:43Z

You can't interact with PHP once the HTML is sent to the browser without either

Refreshing the page, or
Using AJAX (JavaScript).

If you know the options in the <select> beforehand (which it seems like you do), you should write some JavaScript to accomplish what you need. Here is a simple example using jQuery.

$('#tables_select').change(
    function( eventObject ){
        alert('You chose ' + $(this).val());
        switch( $( this ).val())
        {
            case 'Applications':
                $('#tables').append('<input type="text" name="application_name" value="Enter an application name" />"');
            break;
            case 'Device':
                $('#tables').append('<input type="text" name="device_name" value="Enter a device name" />"');
            break;
        }

    }
);

You will need to add additional logic to remove the inserted elements if the user changes their choice, and to insert the correct <input> elements when the page first loads, but it is a good starting point.

Ket. · Accepted Answer · 2012-01-27 05:22:22Z

if you want to add any input type ... here is the demo demo with code
you use following method.

<form method="post" action="<?php echo $PHP_SELF;?>" onChange="return createTxtbox()">
Table Name: <div id="tables">
<select name="tables">
<option value="Applications">Application</option>
<option value="Device">Device</option>
</select>
</div>
<span id="fooBar">&nbsp;</span>
</form>

then write javascript,

<SCRIPT language="javascript">
function createTxtbox() {
 var type="text";
    //Create an input type dynamically.
    var element = document.createElement("input");

    //Assign different attributes to the element.
    element.setAttribute("type", type);
    element.setAttribute("value", type);
    element.setAttribute("name", type);

    var foo = document.getElementById("fooBar");

    //Append the element in page (in span).
    foo.appendChild(element);

}
</SCRIPT>

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