$grid["edit_options"]["beforeSubmit"] = "function(post,form){ return validate_form_once(post,form); }";
$grid["add_options"]["beforeSubmit"] = "function(post,form){ return validate_form_once(post,form); }";
$g->set_options($grid);

And in HTML script tag:

function validate_form_once(post,form)
{
    var str=[];

    if (post.contract_Worth > 10)
        str[str.length] = "- Contract Approve Date is required";

    str = str.join("<br>");

    if (str.length == 0)
        return [true,""];
    else
        return [false,"Check following errors:<br>"+str];
}