How to use the @iota/transaction.lastIndex function in @iota/transaction

}

    if (issuanceTimestamp && issuanceTimestamp.length > ISSUANCE_TIMESTAMP_LENGTH) {
        throw new RangeError(errors.ILLEGAL_ISSUANCE_TIMESTAMP_LENGTH)
    }

    if (tag && tag.length > TAG_LENGTH) {
        throw new RangeError(errors.ILLEGAL_TAG_LENGTH)
    }

    const signatureOrMessageCopy = signatureOrMessage
        ? signatureOrMessage.slice()
        : new Int8Array(SIGNATURE_OR_MESSAGE_LENGTH)
    const numberOfFragments = signatureOrMessageCopy.length / SIGNATURE_OR_MESSAGE_LENGTH
    const bundleCopy = new Int8Array(bundle.length + numberOfFragments * TRANSACTION_LENGTH)
    const currentIndexBuffer = bundle.length > 0 ? increment(lastIndex(bundle)) : new Int8Array(LAST_INDEX_LENGTH)
    const lastIndexBuffer = currentIndexBuffer.slice()
    let fragmentIndex = 0

    bundleCopy.set(bundle.slice())

    // Create and append transactions to the bundle.
    for (let offset = bundle.length; offset < bundleCopy.length; offset += TRANSACTION_LENGTH) {
        const signatureOrMessageCopyFragment = signatureOrMessageCopy.subarray(
            fragmentIndex * SIGNATURE_OR_MESSAGE_LENGTH,
            (fragmentIndex + 1) * SIGNATURE_OR_MESSAGE_LENGTH
        )

        bundleCopy.set(signatureOrMessageCopyFragment, offset + SIGNATURE_OR_MESSAGE_OFFSET)

        if (address) {
            bundleCopy.set(address, offset + ADDRESS_OFFSET)