Jquery before submitting the form

Question

I have a list, (a simple list) from which i am able to select and set elements (using js), and then a form that allows me to choose how many elements i want, and a submit form.if one doesn't select an element, there is a script that throws an exception. The problem is that i want that the form doesn't submit, if an element is not selected, but not throw an exception, but to show me a message down the submit button (using jquery). my script below:

<? foreach ($types as $type):?>
<ul class = "product_types">
    <? if ($type->stock_2 > 0):?>
    <li id = 'product_types'><a href="#" onclick='selecteazaElement(<?= $type->id; ?>,<?= $type->stock_2; ?>);'><?= $type->label; ?></a></li>
    <? else: ?>
    <li id = 'product_unavailable_types'><label><?= $type->label; ?></label></li>
    <? endif; ?>

</ul>
<? endforeach; ?>
<form  name="addtobasket" method="POST" action="<?= Route::url('Add to Basket', array('sale_id' => $sale->id)); ?>">
    <input type="hidden" name="idOfSelectedItem" id="idOfSelectedItem" value="-1">
    <select name="number" id="number">
        <option value=0>Alege numarul de produse</option>    </select>
    <button type="submit" name = "submit" onclick="addtobasket";>Adauga in cos</button><br />
</form>

and the js that sets the list elements:

   <script type="text/javascript">
   function selecteazaElement(id,stock)
    {
   document.addtobasket.idOfSelectedItem.value=id;
   window["canSubmit"] = true;
   var number23=document.addtobasket.number;
   number23.options.length=0;
   if (stock>=6)
   stock=6;
   for (i=1;i<=stock;i++)
    {
//alert ('id: '+id+'; stock: '+stock);
   number23.options[number23.options.length]=new Option(i, i);
   }
//window.status="my status";
}

Answer 1

Add a submit listener to the form. When it's submitted, check to see if an element is selected, and if not you can prevent the submission by using return false. Here's an example:

$('#myForm').submit(function()
{
    if (/* test case not true */) { 
        $('#myError').show();
        return false; 
    }

    // ... continue work
});

And here's the HTML:

<form id="myForm">
    <input type="text"/>
    <input type="submit"/>
</form>

If you don't want to use jQuery, you can also handle the submit event with plain JavaScript like so:

var myform = document.getElementById('myForm');
myform.addEventListener('submit', function() { console.log('Submitted!'); return false; });