web3-utils#soliditySha3 TypeScript Examples

/**
   * Specific hash function based on keccak256. Hashes similarly to functions from a merkle contract.
   * @param arg two values to hash. Each value takes 32 byte.
   */
  private static merkleKeccak256(arg: Uint8Array): string {
    const first = `0x${(<Buffer>arg).toString('hex').slice(0, 64)}`;

    const second = `0x${(<Buffer>arg).toString('hex').slice(64)}`;
    let res;

    if (new BigNumber(first).lt(second)) {
      res = soliditySha3(first, second);
    } else {
      res = soliditySha3(second, first);
    }

    return res.slice(2);
  }

/**
   * Calculates the proof for a refund, sends a refund transaction. If successful, notifies the backend of a successful refund.
   * @param promotionId promotion id to refund.
   * @param onTransactionHash a function to be called after sending a refund transaction.
   * @return stream that emits the transaction hash once and completes.
   */
  public refund(
    promotionId: number,
    onTransactionHash?: (hash: string) => void
  ): Observable<string> {
    const address = this.authService.userAddress;
    return from(this.checkChain()).pipe(
      filter(success => success),
      switchMap(() => this.gasRefundApiService.getPromotionMerkleData(promotionId)),
      switchMap(({ leaves, rootIndex, amount }) => {
        // leaf is keccak256(abi.encodePacked(address, weiAmount))
        const leaf = soliditySha3(address, amount.toFixed(0));

        const tree = new MerkleTree(leaves, GasRefundService.merkleKeccak256);
        const root = `0x${tree.getRoot().toString('hex')}`;
        const proof = tree.getHexProof(leaf);

        return from(this.sendRefund(proof, amount, { root, rootIndex }, onTransactionHash)).pipe(
          map(receipt => ({ txHash: receipt.transactionHash, leaf }))
        );
      }),
      switchMap(({ txHash, leaf }) => {
        return this.gasRefundApiService.markPromotionAsUsed(txHash, leaf).pipe(map(() => txHash));
      })
    );
  }

export function loadTree(balances, decimals = 18) {
    const elements: any = [];
    Object.keys(balances).forEach((address) => {
        const balance = scale(balances[address], decimals);
        const leaf = soliditySha3(address, balance);
        elements.push(leaf);
    });
    return new MerkleTree(elements);
}

leaf = soliditySha3(recipient, scaledBalance)