smart capture javascript validation

Question

I tried to do validation using Javascript on smart capture. When I submit the form it does not seem that the function is running.

My code:

Form tag:

<form id="myId" class="smartcapture-content-wrapper fuelux" onsubmit="return valid();" novalidate="novalidate">

Javascript function:

<script>
function valid() {
    if(SOME IF)
    {
        return false;   
    }
    return true;

}
</script>

How can I make it work?

Is there another way to do the validation?