Dipswitch generator

//variables
        var off = 'dip0';

        //methods to confirm a numeric entry
        function isNumberKey(evt){
            var charCode = (evt.which) ? evt.which : event.keyCode
            if (charCode > 31 && (charCode < 48 || charCode > 57))
                return false;
            return true;
        }

        function isNumeric(n) {
                return !isNaN(parseFloat(n)) && isFinite(n);
        }

        //method to flip the switch
        function invert(){
            if (off == 'dip1'){
            document.getElementById("invertbutton").src = "images/software/dipswitch/down.png";
            off = 'dip0';
            }else{
            document.getElementById("invertbutton").src = "images/software/dipswitch/up.png";
            off = 'dip1';
            }
            convert('decimaltobinair');
        }
        function convert(id){
            if(id == 'decimaltobinair'){ //convert decimal to binary notation
                error('0');
                setBinair(parseInt(getDecimal(), 10).toString(2).split("").reverse().join(""));
                imagecreate(getBinair());
            }else{
                setDecimal(parseInt(getBinair().split("").reverse().join(""), 2));  //convert binary notation to decimal notation
                error('0');
            }
        }
        function imagecreate(binair){
            var binairsplit = binair.split("");
            for (var i=0; i<10; i++){ //loop through switches and set all to "off"
                document.getElementById('dip' + i).className = off;
            }
            for (var i=0; i<binairsplit.length; i++){
                if (off == 'dip1'){
                    if (binairsplit[i] == 1){
                        binairsplit[i] = 0
                    }else{
                        binairsplit[i] = 1
                    }
                }
                document.getElementById('dip' + i).className = 'dip' + binairsplit[i];
            }
        }
        function imagetobinair(id){
            if (document.getElementById(id).className == 'dip0'){ //change dipswitch location
                document.getElementById(id).className = 'dip1';
            }else{
                document.getElementById(id).className = 'dip0';
            }
            var binairimage = ""; //generate binary number based on the switch positions
            for (var i=0; i<10; i++){
                var classnamesplit = document.getElementById('dip' + i).className.split("");
                    if (off == 'dip1'){
                        if ( classnamesplit[3] == '1' ){
                            binairimage = binairimage + '0';
                        }else{
                            binairimage = binairimage + '1';
                        }
                    }else{
                            binairimage = binairimage + classnamesplit[3];
                    }
            }
            setBinair(binairimage);
            convert('binairtodecimal');
        };


        //methods to catch errors
        function error(errorcode){
            if (errorcode == '0'){
                 document.getElementById('error').innerHTML =  "";
            }else if(errorcode == '1') {
                  document.getElementById('error').innerHTML = "Geef aub een nummer in tussen de 0 en 1023";
                  document.getElementById('dmx_binair').value = 'error';
                  imagecreate('0');
            }
        }

        //getters and setters
        function setBinair(value){
            document.getElementById('dmx_binair').value = value;
        }
        function getBinair(){
             return document.getElementById('dmx_binair').value;
        }
        function setDecimal(value){
            document.getElementById('dmx_decimal').value = value;
        }
        function getDecimal(){
            var decimal = document.getElementById('dmx_decimal');
            if (isNumeric(decimal.value) && decimal.value < 1024 && decimal.value >= 0){
                return decimal.value;
            }else{
                error('1');
                return 0;
            }
        }