function MyBigFunctionThatConvertsManyTypes (value, type)
{
  // ...
}

context.registerTypeConversion('xsd:integer', function(x){ MyBigFunctionThatConvertsManyTypes(x, 'integer'); });
context.registerTypeConversion('xsd:double', function(x){ MyBigFunctionThatConvertsManyTypes(x, 'double'); });
context.registerTypeConversion('xsd:dateTime', function(x){ MyBigFunctionThatConvertsManyTypes(x, 'dateTime'); });