javascriptでOptional

Optional.js

var Optional = (value) => {
  var isNull = value === null || value === undefined;
  return {
    filter:(action) => (isNull || !action(value)) ? Optional() : Optional(value),
    map:(action) => isNull ? Optional() : Optional(action(value)),
    isPresent:() => !isNull,
    ifPresent:(action) => {
      if(!isNull) action(value);
    },
    get:() => isNull ? null : value,
    orElse:(other) => isNull ? other : value,
    orElseGet:(action) => isNull ? action() : value,
    orElseThrow:(exceptionSupplier) => {
      if(isNull) throw exceptionSupplier();
      return value;
    }
  };
};
Optional.of = (value) => Optional(value);
Optional.empty = () => Optional();