thing.js

class Thing {
  constructor(val) {
    this.val = val;
  }
  unwrap() {
    throw "unimplemented!";
  }

  is_ok() {
    throw "unimplemented!";
  }

  is_err() {
    throw "unimplemented!";
  }
}

class Ok extends Thing {
  constructor(val) {
    super(val);
  }

  unwrap() {
    return this.val;
  }

  is_ok() {
    console.log("HERE");
    return true;
  }

  is_err() {
    false;
  }
}

class Err extends Thing {
  constructor(val) {
    super(val);
  }

  unwrap() {
    throw this.val;
  }

  is_ok() {
    return false;
  }

  is_err() {
    return true;
  }
}

class Result {
  constructor(val) {
    this.val = val;
  }

  and(val) {
    if (this.val.is_ok() && val.is_ok()) {
      return new Result(val);
    } else {
      if (this.val.is_err()) {
        return new Result(this.val);
      } else if (val.is_err()) {
        return new Result(val);
      }
    }
  }

  and_then(cb) {
    if (this.val.is_ok()) {
      return cb(this.val);
    } else {
      return new Result(this.val);
    }
  }

  or(val) {
    if (this.val.is_ok()) {
      return new Result(this.val);
    } else {
      return new Result(val);
    }
  }

  unwrap() {
    return this.val.unwrap();
  }

  static async wrap(promise) {
    try {
      return new Result(new Ok(await promise));
    } catch (e) {
      return new Result(new Err(e));
    }
  }
}

const R = Result.wrap;

// examples
// const throws = new Promise((_, reject) => reject("blowup"));
const one = new Promise((r, rej) => r(1));
const two = new Promise(r => 2);

// async function unsafeThing() {
//   await R(throws).unwrap();
// }
async function safe() {
  let x = await R(one);
  console.log(x.unwrap());
} // 2
/*async function unsafeToSafe() {
  await R(throws)
    .or(new Ok(2))
    .unwrap();
} // 2*/

// unsafeThing();
console.log(safe());
// unsafeToSafe();

Promise { }
1

Try:

async function unsafeToSafe() {
  return (await R(new Promise((_, reject) => reject("blowup"))))
    .or(new Ok(2))
    .unwrap();
}

unsafeToSafe().then(x => console.log(x))