race-cancellation/dist/newRaceCancel.js

Utilities for using Promise.race([task, cancellation]) for async/await code.

// we are casting the sentinel value to a unique symbol
// to get === union narrowing
const sentinelValue = {
    toString: () => "[cancel sentinel]",
};
/**
 * Create a {@link RaceCancelFn} function.
 *
 * @param isCancelled - a function that returns whether or not we are currently cancelled
 * @param executor - a callback to resolve the cancellation
 * @param cancelReason - an optional reason for the cancellation
 * @public
 */
export default function newRaceCancel(isCancelled, executor, cancelReason) {
    // the async cancel executor should only run 0 or 1 times
    const memoizedAsyncCancel = memoizeAsyncCancel(isCancelled, executor);
    return async (asyncFnOrPromise) => throwIfCancelled(await raceCancel(asyncFnOrPromise, isCancelled, memoizedAsyncCancel), cancelReason);
}
function raceCancel(asyncFnOrPromise, isCancelled, memoizedAsyncCancel) {
    return typeof asyncFnOrPromise === "function"
        ? isCancelled()
            ? memoizedAsyncCancel()
            : Promise.race([asyncFnOrPromise(), memoizedAsyncCancel()])
        : Promise.race([asyncFnOrPromise, memoizedAsyncCancel()]);
}
function throwIfCancelled(result, cancelReason) {
    if (result === sentinelValue) {
        throw intoCancelError(cancelReason);
    }
    return result;
}
function memoizeAsyncCancel(isCancelled, executor) {
    let promise;
    return () => {
        if (promise === undefined) {
            promise = isCancelled()
                ? Promise.resolve(sentinelValue)
                : waitForCancel(executor);
        }
        return promise;
    };
}
async function waitForCancel(cancelExecutor) {
    await new Promise(cancelExecutor);
    return sentinelValue;
}
function intoCancelError(cancelReason) {
    if (typeof cancelReason === "function") {
        cancelReason = cancelReason();
    }
    if (cancelReason === undefined || typeof cancelReason === "string") {
        return newCancelError(cancelReason);
    }
    return cancelReason;
}
function newCancelError(message = "The operation was cancelled") {
    const cancelError = new Error(message);
    cancelError.name = "CancelError";
    cancelError.isCancelled = true;
    return cancelError;
}
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