In the Risk Register I wants to add new field and it might be read only when user create new Risk

[Nayanja]

function onLoad() {

    if (g_form.isNewRecord()) {

        g_form.setReadOnly('u_threat_actor', 'false');

    } else {

        g_form.setReadOnly('u_threat_actor', 'true');

    }

}

checked that it is overriding the business rules, client scripts, and UI policies.

[Nayanja]

But my requirement is the ,that field needs to be read-only new records only