الـ Promises و async/await: sequential و parallel والأخطاء والإلغاء

// Promise: وعد بقيمة هتيجي بعدين
function getUser(id) {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      if (id === 7) resolve({ id, name: "مُنى" });
      else reject(new Error(`user ${id} مش موجود`));
    }, 100);
  });
}

const p = getUser(7);
console.log(p);

p.then((user) => console.log("then:", user.name));
getUser(9)
  .then((user) => console.log(user))
  .catch((err) => console.log("catch:", err.message))
  .finally(() => console.log("finally"));

$ node main.js
Promise { <pending> }
then: مُنى
catch: user 9 مش موجود
finally

const sleep = (ms) => new Promise((resolve) => setTimeout(resolve, ms));
const t0 = Date.now();
const at = () => `${Math.round((Date.now() - t0) / 100) * 100}ms`;


async function getUser(id) {
  await sleep(300);
  if (id !== 7) throw new Error("مش موجود");
  return { id, name: "مُنى" };
}
async function getCourses() {
  await sleep(300);
  return ["Node", "SQL"];
}

async function main() {
  // واحد ورا التاني
  const user = await getUser(7);
  const courses = await getCourses();
  console.log(at(), "sequential:", user.name, courses);

  // مع بعض
  const [u2, c2] = await Promise.all([getUser(7), getCourses()]);
  console.log(at(), "parallel:", u2.name, c2);

  try {
    await getUser(9);
  } catch (err) {
    console.log(at(), "اتمسك:", err.message);
  }
}

main();

$ node main.js
600ms sequential: مُنى [ 'Node', 'SQL' ]
900ms parallel: مُنى [ 'Node', 'SQL' ]
1200ms اتمسك: مش موجود

const sleep = (ms) => new Promise((resolve) => setTimeout(resolve, ms));
const t0 = Date.now();
const at = () => `${Math.round((Date.now() - t0) / 100) * 100}ms`;


const ok = (v, ms) => sleep(ms).then(() => v);
const fail = (msg, ms) => sleep(ms).then(() => { throw new Error(msg); });

const results = await Promise.allSettled([ok("users", 100), fail("payments down", 200), ok("courses", 150)]);
for (const r of results) console.log(r.status, r.value ?? r.reason.message);

try {
  await Promise.all([ok("users", 100), fail("payments down", 200)]);
} catch (err) {
  console.log("all وقعت كلها:", err.message);
}

console.log("race:", await Promise.race([ok("fast", 100), ok("slow", 500)]));
console.log("any:", await Promise.any([fail("a", 50), ok("b", 100), ok("c", 200)]));

$ node main.js
fulfilled users
rejected payments down
fulfilled courses
all وقعت كلها: payments down
race: fast
any: b

async function slowApi(signal) {
  return new Promise((resolve, reject) => {
    const timer = setTimeout(() => resolve("data"), 2000);
    signal?.addEventListener("abort", () => {
      clearTimeout(timer);
      reject(signal.reason);
    });
  });
}

try {
  await slowApi(AbortSignal.timeout(300));
} catch (err) {
  console.log("اتلغى:", err.name);
}

// promise مالهاش catch
async function forgotten() {
  throw new Error("محدش مسكني");
}
forgotten();
console.log("الملف خلص");

$ node main.js
اتلغى: TimeoutError
الملف خلص

file:///home/you/my-backend/main.js:19
  throw new Error("محدش مسكني");
        ^

Error: محدش مسكني
    at forgotten (file:///home/you/my-backend/main.js:19:9)
    at file:///home/you/my-backend/main.js:21:1

Node.js v24.14.1

const sleep = (ms) => new Promise((resolve) => setTimeout(resolve, ms));
const t0 = Date.now();
const at = () => `${Math.round((Date.now() - t0) / 100) * 100}ms`;


const api = {
  user: () => sleep(200).then(() => ({ name: "مُنى" })),
  courses: () => sleep(300).then(() => ["Node", "SQL"]),
  notifications: () => sleep(250).then(() => { throw new Error("notifications down"); }),
  recommendations: () => sleep(5000).then(() => ["Redis"]),
};

const withTimeout = (promise, ms, fallback) =>
  Promise.race([promise, sleep(ms).then(() => fallback)]);

async function loadDashboard() {
  const defaults = { user: null, courses: [], notifications: [], recommendations: [] };
  const keys = Object.keys(api);
  const results = await Promise.allSettled(
    keys.map((k) =>
      k === "recommendations" ? withTimeout(api[k](), 500, []) : api[k](),
    ),
  );
  const data = {};
  const errors = [];
  results.forEach((r, i) => {
    const key = keys[i];
    if (r.status === "fulfilled") data[key] = r.value;
    else {
      data[key] = defaults[key];
      errors.push(key);
    }
  });
  return { data, errors };
}

const { data, errors } = await loadDashboard();
console.log(at());
console.log(data);
console.log("errors:", errors);
process.exit(0);

$ node main.js
500ms
{
  user: { name: 'مُنى' },
  courses: [ 'Node', 'SQL' ],
  notifications: [],
  recommendations: []
}
errors: [ 'notifications' ]