@empathyco/x-components/js/utils/cancellable-promise.js

Empathy X Components

import { noOp } from './function.js';

/**
 * Symbol used to know if a promise is cancelled.
 *
 * @internal
 */
const CancelSymbol = Symbol('cancelled-promise');
/**
 * Util function that returns an object which contains a promise, result of Promise.race call
 * between the original one passed as parameter and another one, created within the function, used
 * for reject in the resultant promise manually. If the cancel method is triggered, the
 * resultant promise is rejected.
 *
 * @remarks The promise function passed as first param executes its own async code ALWAYS although
 * it's cancelled or not. The payload of the resultant promise is the returned by the function that
 * ends first. So, the promise is not cancelled exactly. The parameter first passed to cancel is the
 * resultant promise rejection value.
 *
 * If you need to check if the promise is not being rejected with CancelSymbol (on purpose).
 * You should check the error type in the cancellable catch using the payload.
 *
 * @param promise - Original promise.
 * @param cancelCallback - Optional callback to be called on cancel.
 * @returns CancellablePromiseFunction {@link CancellablePromiseFunction}.
 *
 * @internal
 */
function cancellablePromise(promise, cancelCallback) {
    let cancel = noOp;
    const cancelPromise = new Promise((_, reject) => {
        cancel = payload => {
            reject(CancelSymbol);
            cancelCallback?.(payload);
        };
    });
    return {
        promise: Promise.race([promise, cancelPromise]),
        cancel,
    };
}

export { CancelSymbol, cancellablePromise };
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