Add composition of validators

[Eoksni]

I have a need of composing two validators, ie the value can satisfy either of validators. My use-case is origin url for cors setup - it can either be an actual url or a string '*' to allow any origin.

Here is my take on this:

// #region `oneOf` definition
type MkValidator<T> = (spec?: Spec<T>) => ValidatorSpec<T>;

// helper function to encapsulate usage of internals
function parse<T>(val: ValidatorSpec<T>, x: string): T {
  const res = val._parse(x);
  if (val.choices) {
    if (val.choices.indexOf(res) === -1) {
      throw new Error(
        `Value "${x}" not in choices: [${val.choices.join(", ")}]`
      );
    } else {
      return res;
    }
  } else {
    return res;
  }
}

// define `oneOf` combinator
const oneOf = <T>(
  val: ValidatorSpec<T>,
  ...vals: ValidatorSpec<T>[]
): MkValidator<T> => {
  const all = [val, ...vals];

  // I went with simpler approach to specify all documentary stuff on resulting validator
  // and reject all these properties on sub validators.
  for (const v of all) {
    if (v.default !== undefined) {
      throw new Error(
        `'default' property is not supported in oneOf sub validators.`
      );
    }
    if (v.devDefault !== undefined) {
      throw new Error(
        `'devDefault' property is not supported in oneOf sub validators.`
      );
    }
    if (v.desc !== undefined) {
      throw new Error(
        `'desc' property is not supported in oneOf sub validators.`
      );
    }
    if (v.docs !== undefined) {
      throw new Error(
        `'docs' property is not supported in oneOf sub validators.`
      );
    }
    if (v.example !== undefined) {
      throw new Error(
        `'example' property is not supported in oneOf sub validators.`
      );
    }
  }

  const types = all.map(v => v.type);
  const type = `oneOf: [${types.join(", ")}]`;

  return makeValidator(x => {
    try {
      return parse(val, x);
    } catch (err) {
      const errs = [err];
      for (const v of vals) {
        try {
          return parse(v, x);
        } catch (e) {
          errs.push(e);
          continue;
        }
      }
      throw new Error(
        `oneOf validator failed: [\n${errs.map(e => e.message).join(",\n")}\n]`
      );
    }
  }, type);
};
// #endregion

And here is the usage:

// creating `origin` validator using `oneOf` combinator
const origin = oneOf(url(), str({ choices: ["*"] }));

export default cleanEnv(
  process.env,
  {
    // example usage of newly created validator
    FRONTEND_ORIGIN: origin({
      devDefault: "*",
      example: "http://localhost:3000"
    })
  }
);

[af]

This is a neat trick, but I don't think it's going to be used commonly enough to justify inclusion in the library itself. As a result I'm going to close this issue, but thanks for posting this, I think some people might find it useful 👍