Prime or not

[insane]

This will let you know whether a number is prime or not ..

<style>
body{text-align:center; font-family:arial;}
.answerbox,.detailbox {
       background-color:#FFFFFF; 
       font-size:80;
       height:100;
       color: black;
       font-weight:bold; 
       text-align: center;
       width:950;
       }
       
.detailbox {
       height:80;     
       font-size:50
       }

sup {font-size:40; vertical-align:top; position:relative; top:-5}
      
#quest{
       font-size:20;
       text-align:right;
       border-style: solid;
       border-color: gray;
       border-width: 1;
       width: 130
       }     
</style>
<script>

function power(arr)
  {
  newarr=new Array()
  for(k=0; true; k++)
    {
    base=arr[0]
    for (expo=1; arr[expo]==base;expo++){}
    newarr[k]=base+(expo!=1 ? "<sup>"+expo+"</sup>" : "")
    if (expo>=arr.length) {break}
    arr=arr.slice(expo)  
    }
  return newarr.join("×")
  }

function twodivisors(numb)
  {
  for (var i=2; i<=Math.sqrt(numb); i+=1)
    {
    if (numb%i==0) {return new Array(i,numb/i)}
    }
  return "pr" 
  }

function analyze(num)
  {
  iffalse=detailsplace+"=num+'='+power(primedivisors);"+yesnoplace+"='Number '+num+' is not prime'"
  iftrue=yesnoplace+"='Number '+num+' is prime';"+detailsplace+"=''"
  
  if (num<2) {eval(detailsplace+"='';"+yesnoplace+"='Number '+num+' is not prime'"); return} 
  if (num==2) {eval(iftrue); return}
  
  if (num%2==0)
    {
    primedivisors=new Array()
    primedivisors.push(2)
    for (otherdivisor=num/2; twodivisors(otherdivisor)!="pr"; otherdivisor=twoparts[1])
     {
     twoparts=twodivisors(otherdivisor);
     primedivisors.push(twoparts[0]);
     }
    primedivisors.push(otherdivisor)
    eval(iffalse); return
    }
    
  for (var i=3; i<=Math.sqrt(num); i+=2)
    {
    if (num%i==0) 
     {
     primedivisors=new Array()
     primedivisors.push(i)
     for (otherdivisor=num/i; twodivisors(otherdivisor)!="pr"; otherdivisor=twoparts[1])
      {
      twoparts=twodivisors(otherdivisor);
      primedivisors.push(twoparts[0]);
      }
     primedivisors.push(otherdivisor)
     eval(iffalse); return
     }
    }
  eval(iftrue); return
  }
  
function starter()
  {
  num=document.formh.quest.value
  if (isNaN(num)) {alert("You entered an invalid number."); return}
  detailsplace="document.getElementById('details').innerHTML"
  yesnoplace="document.getElementById('answer').innerHTML"
  analyze(eval(num))
  }  
  
</script>

<div class=answerbox id=answer></div>
<div class=detailbox id=details></div>
<form name=formh>
  Number: <input type=text id=quest><br>
  <input type=button value="Is it prime?" onClick=starter()><br>
</form>