Question

I have a select tag, where users can select what TYPE of exposure they want for their clicks:

 <select name="exposure">
                        <?php while($a = mysql_fetch_assoc($r)):  ?>
                            <option value=""><?php echo $a['exposure']; ?></value>
                        <?php endwhile; ?>
                        </select>

Below that, I have another select tag, that will show the clicks with value taken from whatever exposure type they chose:

<select name="clicks">
                        <?php while($a = mysql_fetch_assoc($r)):  ?>
                            <option value=""><?php echo $a['amount']; ?></value>
                        <?php endwhile; ?>
                        </select>

My question is: How can I change the value in the second select tag, according to whatever the user has chosen in the first?

Answer 1

This shouldn’t be too difficult. All you really need is a mapping between ‘exposure’ values and ‘clicks’ values, and some way to turn the ‘clicks’ values into valid markup. You can play around with the example below on jsFiddle: http://jsfiddle.net/ninjascript/5QPq5/

/**
 * Here's a map of possible values from 'exposure' and
 * related values for 'clicks'.
 */
var map = {
    "OptionA": ['A001','A002','A003'],
    "OptionB": ['B001','B002','B003']  
};

/** 
 * A quick and dirty method to turn some values in the map
 * into a set of <option> tags.
 */
function create(key)
{
    var result = [];
    if (map.hasOwnProperty(key)) {
        for (var i = 0; i < map[key].length; i++) {
            result.push('<option value="'+map[key][i]+'">');
            result.push(map[key][i]);
            result.push('</option>');
        }
    }
    return result.join('');
}

/**
 * Use jQuery to handle every 'change' event and add a new
 * set of <option> elements to the 'clicks' element.
 */
$('select[name="exposure"]').live('change', function()
{   
    var options = create(this.value);
    $('select[name="clicks"]').html(options);
    $('div').html('<span>foo</span>'); // <-- Update some other element too
});

Edit: jQuery.live() will execute a function whenever an event occurs. You can do whatever you want within that function, including change the contents of multiple DOM elements.