Timeouts und Abbrechen mit AbortController

Warum Timeouts und Abbrüche?

Signalüberwachte Aufgabe

// Fake fetch that respects AbortSignal
function fakeFetch(ms, value, signal) {
  return new Promise(function (resolve, reject) {
    // Abort handler
    function onAbort() {
      clearTimeout(t);
      reject(new Error("aborted"));
    }

    // If already aborted
    if (signal && signal.aborted) {
      return reject(new Error("aborted"));
    }

    // Finish timer
    const t = setTimeout(function () {
      if (signal) {
        signal.removeEventListener("abort", onAbort);
      }
      resolve(value);
    }, ms);

    // Listen for abort
    if (signal) {
      signal.addEventListener("abort", onAbort);
    }
  });
}

fakeFetch(5, "OK").then(function (v) {
  console.log("fakeFetch:", v);
});

Abort in Aktion

// AbortController cancels signal-aware tasks
const controller = new AbortController();

fakeFetch(20, "Too slow", controller.signal)
  .then(function (v) {
    console.log("done:", v);
  })
  .catch(function (e) {
    console.log("catch:", e.message);
  });

// Abort after a short delay
setTimeout(function () {
  controller.abort();
  console.log("aborted");
}, 5);

Timeout-Wrapper

// Add a timeout to any Promise with Promise.race
function withTimeout(promise, ms) {
  return Promise.race([
    promise,
    new Promise(function (_resolve, reject) {
      const t = setTimeout(function () {
        reject(new Error("timeout"));
      }, ms);
      // Small trick: clear timer when the main promise settles
      promise.finally(function () { clearTimeout(t); });
    })
  ]);
}

// Demo: this will time out
withTimeout(fakeFetch(30, "late"), 10)
  .then(function (v) { console.log("value:", v); })
  .catch(function (e) { console.log("timeout:", e.message); });

Timeout und Abort zusammen

// Combine: abort if timeout fires
async function fetchWithTimeout(msWork, msTimeout) {
  const c = new AbortController();

  const task = fakeFetch(msWork, "data", c.signal);

  // If timeout wins, abort the task
  try {
    const result = await withTimeout(task, msTimeout);
    return result;
  } catch (e) {
    c.abort();
    throw e;
  }
}

fetchWithTimeout(25, 10)
  .then(function (v) { console.log("got:", v); })
  .catch(function (e) { console.log("failed:", e.message); });

Tipps und Checkliste

Quiz zu den Grundlagen von AbortController

Zusammenfassung