race-cancellation/dist/composeRaceCancel.js

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

import noopRaceCancel from "./noopRaceCancel.js";
/**
 * Returns a {@link RaceCancelFn} function that is the composition of the two RaceCancel functions.
 *
 * @remarks
 * For convenience of writing methods that take cancellations, the params
 * are optional. If a is undefined, then b is retuned, if b is undefined then a
 * is returned, and if they both are undefined a noop race that just invokes
 * the task is returned.
 *
 * The outer scope function is expected to be a wider concern like ctrl-C and the inner a narrower
 * concern like timeout. This way if you catch a error then try to say sleep before a retrying the narrower
 * concern the outer will bail out without even starting the timeout because it is already cancelled.
 *
 * This isn't a hard requirement just things are optimized with that assunmption.
 *
 * @param inner - a {@link RaceCancelFn} function that is the inner function of the composition, in general its cancellation scope should be narrower than the outer scope.
 * @param outer - a {@link RaceCancelFn} function that is the outer function, its scope should be wider or equal to the inner scope.
 * @public
 */
export default function composeRaceCancel(inner, outer) {
    return outer === undefined
        ? inner === undefined
            ? noopRaceCancel
            : inner
        : inner === undefined
            ? outer
            : (asyncFnOrPromise) => typeof asyncFnOrPromise === "function"
                ? outer(() => inner(asyncFnOrPromise)) // lazy if function
                : outer(inner(asyncFnOrPromise));
}
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