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

export const finalizeBundle = (bundle: Int8Array): Int8Array => {
    if (!isMultipleOfTransactionLength(bundle.length)) {
        throw new Error(errors.ILLEGAL_TRANSACTION_BUFFER_LENGTH)
    }

    const sponge = new Kerl()
    const bundleCopy = bundle.slice()
    const bundleHash = new Int8Array(BUNDLE_LENGTH)

    // This block recomputes bundle hash by incrementing `obsoleteTag` field of first transaction in the bundle.
    // Normalized bundle should NOT contain value `13`.
    while (true) {
        // Absorb essence trits to squeeze bundle hash.
        for (let offset = 0; offset < bundle.length; offset += TRANSACTION_LENGTH) {
            sponge.absorb(transactionEssence(bundleCopy, offset), 0, TRANSACTION_ESSENCE_LENGTH)
        }

        // Set new bundle hash value.
        sponge.squeeze(bundleHash, 0, BUNDLE_LENGTH)

        // Stop mutation if essence results to secure bundle.
        if (normalizedBundle(bundleHash).indexOf(MAX_TRYTE_VALUE /* 13 */) === -1) {
            // Essence results to secure bundle.
            break
        }

        // Essence results to insecure bundle. (Normalized bundle hash contains value `13`.)
        bundleCopy.set(
            increment(bundleCopy.subarray(OBSOLETE_TAG_OFFSET, OBSOLETE_TAG_OFFSET + OBSOLETE_TAG_LENGTH)),
            OBSOLETE_TAG_OFFSET
        )