To produce random unique numbers by javascript

HTML Structure:

<label>Enter the Max limit random valuelabel>
<input type="text" value="" id="txtmaxvalue"/><br/>
<input type="button" value="Keep clicking me to get random values" onclick="randomise()"/>
<div id="showme">div>

Javascript code:

var rndno;
var arraylist = [];
var showme = document.getElementById("showme");
var hasvalue = false;

function randomise() {
    var maxvalue = document.getElementById("txtmaxvalue").value;
    findnumber(maxvalue);
    showme.innerHTML = "";
    for (var i = 0; i < arraylist.length; i++) {
        showme.innerHTML = showme.innerHTML + arraylist[i] + ", ";
    }
}

function findnumber(maxvalue) {
    rndno = Math.random();
    rndno = Math.floor(rndno * maxvalue);
    for (var k = 0; k < arraylist.length; k++) {
        if (arraylist[k] == rndno) {
            hasvalue = true;
            break;
        }
        else {
            hasvalue = false;
        }
    }
    if (!hasvalue) arraylist.push(rndno);
}

You can see the demo here