Text field and readonly with JS

[hpl]

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.

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;
		}