por alli econtre un random espero te sirva
Código:
random()
var ranNum= Math.round(Math.random()*4);
return ranNum;
function getaQuote()
var whichQuote=get_random();
var quote=new Array(5)
quote[0]="I love JavaScript..sometimes.";
quote[1]="Why are you pushing my button?";
quote[2]="The button you pushed can\'t push you back. You bully, you!";
quote[3]="This alert is here to inform you that alerts are annoying.";
quote[4]="Which came first, the button or the alert?";
alert(quote[whichQuote]);
//-->
</SCRIPT>
</HEAD>
<BODY>
<FORM name="form1">
<INPUT TYPE="button" value="Get a Quote!" onClick="getaQuote()">
</FORM>
</BODY>
este random tiene 4 opciones una menos y es tu ejemplo...
nos vemos