trying to sum all elements in the array "number" have in shown in the form "output" when user clicks on the button, im using a example i found on the net but cant seem to make it owrk or any other example if any can pls help me to understand thanks

[COLOR="#EE82EE"]<body>
<script type="text/javascript">
var number = [];

Array.prototype.sum = function()
{
for (var i = 0, L = this.length, sum = 0; i < L; sum += this[i++]);
return sum(document.getElementById("output").value);
}


function myFunction() {
var x = document.getElementById("box");
number.push(document.getElementById("input").value);
x.innerHTML = number.join('<br/>');
}

function myReset() {
number=[]
number.splice(0);
var x = document.getElementById("box");
x.innerHTML = "";
x.innerHTML = number.join('<br/>');
}

</script>

<form>
<input id="input" type=text>
<input type=button onclick="myFunction()" value="Add to list"/>
</form>

<div id="box" style="border:1px solid black;width:150px;height:150px;overflow:scroll">
</div>
<form>
<input type=button onclick="number.sum()" value="Calculate"/>
<input type=button onclick="myReset()" value="Reset" /> </br></br>
<b>Total(sum):</b></br>
<input id="output" type=text>
</form>
</body>