[code=javascript]
function check_2(evt)
{
    var charCode = (evt.which) ? evt.which : evt.keyCode;
		if (charCode > 32 && charCode < 48)
            return false;
		if (charCode > 49)
			return false;
        return true;
}

function check_8(evt)
{
    var charCode = (evt.which) ? evt.which : evt.keyCode;
		if (charCode > 32 && charCode < 48)
            return false;
		if (charCode > 55)
			return false;
        return true;
}

function check_10(evt)
{
    var charCode = (evt.which) ? evt.which : evt.keyCode;
		if (charCode > 32 && charCode < 48)
            return false;
		if (charCode > 57)
			return false;
        return true;
}

function check_16(evt)
{
   var charCode = (evt.which) ? evt.which : evt.keyCode;
		if (charCode > 32 && charCode < 48)
            return false;
		if (charCode > 57 && charCode < 65)
			return false;
		if (charCode > 70 && charCode < 97)
            return false;	
		if (charCode > 102)
			return false;	
        return true;
}

function check_x(evt)
{
   var charCode = (evt.which) ? evt.which : evt.keyCode;
		if (charCode > 32 && charCode < 48)
            return false;
		if (charCode > 57 && charCode < 65)
			return false;
		if (charCode > 70 && charCode < 97)
            return false;		
		if (charCode > 111)
			return false;	
        return true;
}

function getallen()
{
var bin = document.formulier.bin.value;
var oct = document.formulier.oct.value;
var dec = document.formulier.dec.value;
var hex = document.formulier.hex.value;
var ei = document.formulier.ei.value;
var eigen = document.formulier.eigen.value;

if (bin!="") {	
// BIN_DEC
	var grootte = bin.length;
	var bin_dec = new Array();
	for (i=0; i<grootte; i++) {
	bin_dec[i] = bin.charAt(i); }
	var bin_dec = bin_dec.reverse();
	for (i=0; i<grootte; i++) {
	var dec = Number(dec + bin_dec[i]*Math.pow(2,i)); }
	document.formulier.dec.value=(dec);
	}

if (oct!="") {
// OCT_DEC			
	var grootte = oct.length;
	var oct_dec = new Array();
	for (i=0; i<grootte; i++) {
	oct_dec[i] = oct.charAt(i); }
	var oct_dec = oct_dec.reverse();
	for (i=0; i<grootte; i++) {
	var dec = Number(dec + oct_dec[i]*Math.pow(8,i)); }
	document.formulier.dec.value=(dec);
	}

if (hex!="") {
// HEX_DEC
	var grootte = hex.length;
	var cijfers = new Array();
	for (i=0; i<grootte; i++) {
	cijfers[i] = hex.charAt(i);
	if (cijfers[i]=="A" || cijfers[i]=="a") {
	cijfers[i]=10; }
	else if (cijfers[i]=="B" || cijfers[i]=="b") {
	cijfers[i]=11; }
	else if (cijfers[i]=="C" || cijfers[i]=="c") {
	cijfers[i]=12; }
	else if (cijfers[i]=="D" || cijfers[i]=="d") {
	cijfers[i]=13; }
	else if (cijfers[i]=="E" || cijfers[i]=="e") {
	cijfers[i]=14; }
	else if (cijfers[i]=="F" || cijfers[i]=="f") {
	cijfers[i]=15; }
	}
	var cijfers = cijfers.reverse();
	var dec = 0;
	for (i=0; i<grootte; i++) 
	{
	var temp = (cijfers[i]*Math.pow(16,i));
	var dec = Number(dec + temp);
	}
	document.formulier.dec.value=(dec);
	}
	
if (ei!="" && eigen!="") {
// X_DEC
	var grootte = eigen.length;
	var cijfers = new Array();
	
	for (i=0; i<grootte; i++)
	{
	cijfers[i] = eigen.charAt(i);
	if (cijfers[i]=="A" || cijfers[i]=="a") {
	cijfers[i]=10; }
	else if (cijfers[i]=="B" || cijfers[i]=="b") {
	cijfers[i]=11; }
	else if (cijfers[i]=="C" || cijfers[i]=="c") {
	cijfers[i]=12; }
	else if (cijfers[i]=="D" || cijfers[i]=="d") {
	cijfers[i]=13; }
	else if (cijfers[i]=="E" || cijfers[i]=="e") {
	cijfers[i]=14; }
	else if (cijfers[i]=="F" || cijfers[i]=="f") {
	cijfers[i]=15; }
	else if (cijfers[i]=="G" || cijfers[i]=="g") {
	cijfers[i]=16; }
	else if (cijfers[i]=="H" || cijfers[i]=="h") {
	cijfers[i]=17; }
	else if (cijfers[i]=="I" || cijfers[i]=="i") {
	cijfers[i]=18; }
	else if (cijfers[i]=="J" || cijfers[i]=="j") {
	cijfers[i]=19; }
	else if (cijfers[i]=="K" || cijfers[i]=="k") {
	cijfers[i]=20; }
	else if (cijfers[i]=="L" || cijfers[i]=="l") {
	cijfers[i]=21; }
	else if (cijfers[i]=="M" || cijfers[i]=="m") {
	cijfers[i]=22; }
	else if (cijfers[i]=="N" || cijfers[i]=="n") {
	cijfers[i]=23; }
	else if (cijfers[i]=="O" || cijfers[i]=="o") {
	cijfers[i]=24; }
	else if (cijfers[i]=="P" || cijfers[i]=="p") {
	cijfers[i]=25; }
	}
	var cijfers = cijfers.reverse();
	var dec = 0;
	for (i=0; i<grootte; i++) 
	{
	var temp = (cijfers[i]*Math.pow(ei,i));
	var dec = Number(dec + temp);
	}
	document.formulier.dec.value=(dec);
	}

if (bin=="") {
// DEC_BIN
	var dec1 = dec;
	var stappen = 80;
	for (i=stappen; i>=0; i= i - 1)
	{
	 if (dec1>=Math.pow(2,i)) {
	  bin += "1";
	  dec1 = dec1-Math.pow(2,i); }
	 else {
	  bin += "0"; }
	}
	var first = bin.indexOf('1');
	bin = bin.substring(first);
	document.formulier.bin.value=(bin);
	}

var dec = document.formulier.dec.value;	
if (oct=="") {
// DEC_OCT
	var dec1 = dec;
	var grootte = dec1.length;
	for (i=grootte; i>=0; i--) 
	{
	var macht = Math.pow(8,i);
	if (dec1>=macht) {
	jan = dec1/macht;
	jan = Math.floor(jan);
	
	var oct = oct + jan;
	jan = jan*macht;
	dec1 = dec1-jan;
	}
	else if(dec1<macht) {
	oct = oct + 0; }
	}
	while ( oct.charAt(0) == "0") {
	oct = oct.substring(1); }
	document.formulier.oct.value=(oct);
	}

if (hex=="") {
// DEC_HEX
var dec1 = dec;
	var grootte = dec1.length;
	for (i=grootte; i>=0; i--) 
	{
	var macht = Math.pow(16,i);
	if (dec1>=macht) {
	jan = dec1/macht;
	jan = Math.floor(jan);
	var jan1 = jan;
	if (jan=="10") {
	jan = "A"; }
	else if (jan=="11") {
	jan = "B"; }
	else if (jan=="12") {
	jan = "C"; }
	else if (jan=="13") {
	jan = "D"; }
	else if (jan=="14") {
	jan = "E"; }
	else if (jan=="15") {
	jan = "F"; }
	
	var hex = hex + jan;
	jan1 = jan1*macht;
	dec1 = dec1-jan1;
	}
	else if(dec1<macht) {
	hex = hex + 0; }
	}
	while ( hex.charAt(0) == "0") {
	hex = hex.substring(1); }
	document.formulier.hex.value=(hex);
	}

if (ei!="" && eigen=="") {
// DEC_X
	var jan;
	var grootte = dec.length;
	for (i=grootte; i>=0; i--)
	{
	var macht = Math.pow(ei,i);
	if (dec>=macht) {
	jan = dec/macht;
	jan = Math.floor(jan);
	var jan1 = jan;
	if (jan=="10") {
	jan = "A"; }
	else if (jan=="11") {
	jan = "B"; }
	else if (jan=="12") {
	jan = "C"; }
	else if (jan=="13") {
	jan = "D"; }
	else if (jan=="14") {
	jan = "E"; }
	else if (jan=="15") {
	jan = "F"; }
	else if (jan=="16") {
	jan = "G"; }
	else if (jan=="17") {
	jan = "H"; }
	else if (jan=="18") {
	jan = "I"; }
	else if (jan=="19") {
	jan = "J"; }
	else if (jan=="20") {
	jan = "K"; }
	else if (jan=="21") {
	jan = "L"; }
	else if (jan=="23") {
	jan = "M"; }
	else if (jan=="24") {
	jan = "N"; }
	else if (jan=="25") {
	jan = "O"; }
	
	var eigen = eigen + jan;
	jan1 = jan1*macht;
	dec = dec-jan1;
	
	}
	else if(dec<macht) {
	eigen = eigen + 0; }
	}
		while ( eigen.charAt(0) == "0") {
		eigen = eigen.substring(1); }
		document.formulier.eigen.value=(eigen);
	}
}
//-->


[code=html4strict]
<form name="formulier" action="">
<table width="200" border="0">
  <tr>
    <td><label for="bin">2</label></td>
    <td><input name="bin" type="text" onkeypress="return check_2(event)" id="bin" class="tekstbox" onfocus="this.className='tekstbox_on'" onblur="this.className='tekstbox'" /></td>
  </tr>
  <tr>
    <td><label for="oct">8</label></td>
    <td><input name="oct" type="text" onkeypress="return check_8(event)" id="oct" class="tekstbox" onfocus="this.className='tekstbox_on'" onblur="this.className='tekstbox'" /></td>
  </tr>
  <tr>
    <td><label for="dec">10</label></td>
    <td><input name="dec" type="text" onkeypress="return check_10(event)" id="dec" class="tekstbox" onfocus="this.className='tekstbox_on'" onblur="this.className='tekstbox'" /></td>
  </tr>
  <tr>
    <td><label for="hex">16</label></td>
    <td><input name="hex" type="text" onkeypress="return check_16(event)" id="hex" class="tekstbox" onfocus="this.className='tekstbox_on'" onblur="this.className='tekstbox'" /></td>
  </tr>
  <tr>
    <td><input type="text" name="ei" id="ei" maxlength="2" size="2" class="tekstbox" onfocus="this.className='tekstbox_on'" onblur="this.className='tekstbox'" /></td>
    <td><input name="eigen" type="text" id="eigen" onkeypress="return check_x(event)" class="tekstbox" onfocus="this.className='tekstbox_on'" onblur="this.className='tekstbox'"  /></td>
  </tr>
  <tr>
    <td>&nbsp;</td>
    <td><input type="button" class="button" onclick="getallen()" value="Bereken" />
      <input type="reset" class="button" value="Wissen"/></td>
  </tr>
</table></form>