Beginner Exercism • javascript
Promises

Challenge Overview

The two objectives of this exercise are :
💡 View Solution
export const promisify = (fn) => {
  return (...args) => {
    return new Promise((resolve, reject) => {
      fn(...args, (err, data) => {
        if (err) reject(err);
        else resolve(data);
      });
    });
  };
};

export const all = (promises) => {
  return new Promise((resolve, reject) => {
    if (promises.length === 0) resolve([]);
    const results = [];
    let completed = 0;
    promises.forEach((p, i) => {
      Promise.resolve(p).then(val => {
        results[i] = val;
        completed++;
        if (completed === promises.length) resolve(results);
      }).catch(reject);
    });
  });
};

export const allSettled = (promises) => {
  return new Promise((resolve) => {
    if (promises.length === 0) resolve([]);
    const results = [];
    let completed = 0;
    promises.forEach((p, i) => {
      Promise.resolve(p).then(val => {
        results[i] = { status: 'fulfilled', value: val };
      }).catch(err => {
        results[i] = { status: 'rejected', reason: err };
      }).finally(() => {
        completed++;
        if (completed === promises.length) resolve(results);
      });
    });
  });
};

export const race = (promises) => {
  return new Promise((resolve, reject) => {
    promises.forEach(p => Promise.resolve(p).then(resolve).catch(reject));
  });
};

export const any = (promises) => {
  return new Promise((resolve, reject) => {
    if (promises.length === 0) resolve();
    const errors = [];
    let rejectedCount = 0;
    promises.forEach((p, i) => {
      Promise.resolve(p).then(resolve).catch(err => {
        errors[i] = err;
        rejectedCount++;
        if (rejectedCount === promises.length) {
          reject(new AggregateError(errors, 'All promises were rejected'));
        }
      });
    });
  });
};