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Example usage: Bridge from EVM to Chromia and vice versa

Bridge from EVM to Chromia​

  • Approve token spending​

    Ensure the user approves token spending by the token bridge:

    const approvalResponse = await bcl.approveDepositAmount(BigInt(10));

  • Bridge from EVM to Chromia​

    To bridge tokens from EVM to Chromia, use the depositToEvmBridgeContract method, specifying the number of tokens to bridge:

    const contractTransactionResponse = await bcl.depositToEvmBridgeContract(BigInt(100));

    If the user has created an FT4 account and linked it to their EVM address, funds for foreign tokens will be minted directly to that account. For native tokens, funds will be transferred from the bridge account to the user's account.

    If the user hasn't created an account, or has created one but hasn't linked it to their EVM address, funds for foreign tokens will be minted to the pool account instead. For native tokens, funds will be transferred from the bridge account to the pool account. In this case, the user must create and link an FT4 account. Once this is done, the funds will be transferred from the pool account to the user's account.

  • After a deposit, link the EVM account with the corresponding FT4 account created during the deposit process. Provide the evmKeyStore you created earlier:

    const accountLinkingResponse = await bcl.linkEvmEoaAccount(evmKeyStore);
    note

    If the EVM account is linked, it will be returned to the accountLinkingResponse. An EVM account can have multiple FT4 accounts linked to it.

Bridge from Chromia to EVM​

  • Bridge from Chromia​

    Call the bridgeFromChromia method with the amount and the asset ID:

    // Network ID does not need to be provided as it will be fetched from the provider
    const transactionResponse = await bcl.bridgeFromChromia(BigInt(10), Buffer.from("YOUR_ASSET_ID", "hex"));

Request withdrawal from EVM bridge​

  • Create a pending withdrawal request​

    This needs to be accepted by the user to start the withdrawal process using the requestEvmWithdraw method:

    const erc20WithdrawalInfo = await bcl.getErc20WithdrawalByTransactionRid(
      transactionResponse.receipt.transactionRid,
      opIndex
    );
    // Get event proof for withdrawal
    const eventProof = await bcl.getWithdrawRequestEventProof(erc20WithdrawalInfo.event_hash);
    // Request withdrawal
    const requestedWithdraw = await bcl.requestEvmWithdraw(eventProof);

  • Check withdrawal status​

    Depending on the bridge contract configuration, the user must wait a certain number of blocks on EVM to complete their withdrawal. This can be done using the getPendingWithdrawFromProof method:

    const { block_number } = await getPendingWithdrawFromProof(eventProof);

    Once the block_number has been reached on the target EVM chain, the user can withdraw their tokens:

    const withdrawal = await bcl.evmWithdraw(eventProof.leaf as Buffer);

Additional methods​

  • getErc20Deposits(filter?: DepositFilter, pageSize?: number, pageCursor?: string): Returns all deposits specified by the filter.
  • getErc20Withdrawals(filter?: WithdrawFilter, pageSize?: number, pageCursor?: string): Returns all withdrawals from the EVM bridge specified by the filter.
  • setBlockchainRid(blockchainRid: Buffer): Sets the blockchain RID.