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    Module xflight

    xflight

    Avoid redundant async calls by sharing inflight promises for the same key.

    xflight is a lightweight Node.js utility that manages inflight promises by key. It ensures that only one asynchronous operation per key is running at a time, returning the same promise for concurrent requests. This is useful for avoiding duplicate network or resource-intensive calls.

    • Prevents duplicate async operations for the same key
    • Tracks start and check times for inflight items
    • Cleans up after promise resolution or rejection
    • 100% test coverage
    npm install xflight

    This package requires Node.js >= 22.18.

    import Inflight from "xflight";

    const inflight = new Inflight();

    function fetchData(url) {
      return inflight.promise(url, () => fetch(url));
    }

    // Multiple calls with the same URL will share the same promise if still pending
    fetchData("https://api.example.com/data").then(console.log);
    fetchData("https://api.example.com/data").then(console.log);

    import Inflight from "xflight";

    const inflight = new Inflight();
    const key = "resource-1";

    // Deduplicate async calls
    const resultPromise = inflight.promise(key, () => fetch("https://api.example.com/data"));

    const Inflight = require("xflight").default;

    const inflight = new Inflight();
    // ... use as shown in examples above

    See the full API reference for every option, type, and runtime rule.

    new Inflight([PromiseImpl])

    • PromiseImpl (optional): Custom Promise implementation, e.g. AveAzul. Defaults to the native Promise.

    Note: The constructor does not look for a Promise library. With no argument it uses globalThis.Promise; pass an implementation to use a different one:

    import AveAzul from "aveazul";

    const inflight = new Inflight(AveAzul);

    promise(key, promiseFactory)

    • key: Unique identifier for the inflight operation.
    • promiseFactory: Function that returns a promise.
    • Returns: The promise from promiseFactory, or the existing inflight promise for the key.

    add(key, value, [now])

    • Manually add an inflight item. value should be a promise.

    get(key)

    • Get the current inflight promise for a key, or undefined.

    remove(key)

    • Remove an inflight item by key.

    isEmpty

    • Boolean: true if no inflight items.

    count

    • Number of inflight items.
    • getStartTime(key): Get start time (ms since epoch) for a key.
    • time(key, [now]) / elapseTime(key, [now]): Elapsed time since start.
    • getCheckTime(key): Get last check time for a key.
    • lastCheckTime(key, [now]) / elapseCheckTime(key, [now]): Elapsed time since last check.
    • resetCheckTime(key, [now]): Reset last check time to now.

    To run tests:

    npm test

    Coverage runs with npm run coverage (vitest + v8) and is at 100%.

    import Inflight from "xflight";

    const inflight = new Inflight();
    const key = "resource-1";

    // Deduplicate async calls
    const resultPromise = inflight.promise(key, () => fetch("https://api.example.com/data"));
    // or, for clarity:
    const resultPromise2 = inflight.promise(key, function promiseFactory() {
      return fetch("https://api.example.com/data");
    });

    const promise = new Promise((resolve) => setTimeout(() => resolve("done"), 100));
    inflight.add("manual-key", promise);
    const inflightPromise = inflight.get("manual-key"); // Promise<string> | undefined

    inflight.remove("manual-key");

    console.log(inflight.isEmpty); // true or false
    console.log(inflight.count);   // number of inflight items

    inflight.add("timed-key", new Promise(() => {}));
    const start = inflight.getStartTime("timed-key");
    const elapsed = inflight.time("timed-key");
    const elapsedAlias = inflight.elapseTime("timed-key");

    const check = inflight.getCheckTime("timed-key");
    const sinceLastCheck = inflight.lastCheckTime("timed-key");
    const sinceLastCheckAlias = inflight.elapseCheckTime("timed-key");

    // Reset for a specific key
    inflight.resetCheckTime("timed-key");
    // Reset for all inflight items
    inflight.resetCheckTime();

    Apache-2.0

    © Joel Chen

    Inflight
    InflightStore
    InflightItem
    PromiseFactory
    RecordKey
    Timestamp
    default → Inflight

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