cancel = async function cancel(options = {}) {
    const state = this.state;
    const { copyId } = state;
    if (state.isCompleted) {
        return makeBlobBeginCopyFromURLPollOperation(state);
    }
    if (!copyId) {
        state.isCancelled = true;
        return makeBlobBeginCopyFromURLPollOperation(state);
    }
    // if abortCopyFromURL throws, it will bubble up to user's poller.cancelOperation call
    await state.blobClient.abortCopyFromURL(copyId, {
        abortSignal: options.abortSignal,
    });
    state.isCancelled = true;
    return makeBlobBeginCopyFromURLPollOperation(state);
}
Note: Intentionally using function expression over arrow function expression
so that the function can be invoked with a different context.
This affects what `this` refers to.
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