Function stopped working

I had this function working where it returned a number based on a postcode – it no longer works and I don’t understand why.

(function(){
switch((new String(fieldname46)).toUpperCase())
{
case 'B': return '176.40';
case 'CV': return '181.80';
case 'DE': return '127.50';
case 'DN': return '179.40';
case 'DY': return '181.80';
case 'HD': return '201.30';
case 'HX': return '214.80';
case 'LE': return '158.40';
case 'LU': return '285.00'
case 'LS': return '201.30';
case 'M': return '222.30';
case 'MK': return '213.60';
case 'NG': return '144';
case 'NN': return '196.50';
case 'PE': return '210';
case 'S': return '177.60';
case 'SK': return '207.30';
case 'ST': return '165.30';
case 'WK': return '195.90';
case 'WR': return '212.40';
case 'WS': return '172.80';
case 'WV': return '177.60';
case 'YO': return '217.20';

default: return fieldname47;
}
})();