Text field and readonly with JS

Is it possible to make a function with JS that make a text field readonly? I have tried to use disabled, but if I use this I can read the input with a request.

Code:

---

if (kom==10 || kom==11 || kom==12 || kom==13 || kom==14) {
                        document.forside.elements('l1'+j).disabled=false;
                        document.forside.elements('l2'+j).disabled=false;
                }

---

You can alter the HTML attribute 'readOnly' using client-side scripting.

E.g.

Code:

---

document.forms('formname').object.readOnly=true;

---