Make Contact Mandatory on Opportunity Records

It does not appear this can be achieved through SuiteBuilder and I know workflows won't work at the line level, so I am hoping there is a script to make this happen.  Any suggestions?  This is what I currently have, but I am not getting the desired result.

function saveRecord()
{
    //  Check to see that contact is populated. If not, block the save and warn with a popup.
       
    if (String(nlapiGetFieldValue('contact')).length == 0)
    {
        alert("Please provide a value for contact");
        return false;
    }
    {
        alert("Are you sure you want to Save the record?");
        return true;
}
}