JavaScript - Crear un generador de codigo

<script type="text/javascript">

// <![CDATA[

function test(n) {

var text = "";

var rand = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";

for (var i = 0; i < 5; i++) {

text += rand.charAt(Math.floor(Math.random() * rand.length));

}

n.value = text;

}

// ]]>

</script>

<input type="text" size="4" maxlength="5" onfocus="test(this)"> - <input type="text" size="4" maxlength="5" onfocus="test(this)"> - <input type="text" size="4" maxlength="5" onfocus="test(this)"> - <input type="text" size="4" maxlength="5" onfocus="test(this)"> - <input type="text" size="4" maxlength="5" onfocus="test(this)">