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Introduction

Explanation

Introduction

RenVM is an open protocol for connecting cryptocurrencies and decentralized apps across different blockchains.

RenJS is the official JavaScript/TypeScript library for integrating with RenVM, allowing developers to build cross-chain applications.

Example

Moving an asset like BTC to Ethereum involves minting renBTC, an ERC20 token on Ethereum. When 1 BTC is locked on Bitcoin, 1 renBTC is minted on Ethereum which can be redeemed at any time for BTC again.

Installing

Start by installing RenJS using npm or yarn, along with the collection of modules for connecting to various chains:

yarn add @renproject/ren @renproject/chains

You can now import RenJS and the handlers for each chain, and initialize them with the desired network. (See the Quick Start page, or the Ethereum and Solana docs for how to initialize their providers and signers)

// Import RenJS and chains.
import RenJS from "@renproject/ren";
import { Bitcoin, Ethereum, Solana } from "@renproject/chains";

// Initialize each chain.
const bitcoin = new Bitcoin({ network: "testnet" });
const ethereum = new Ethereum({ network: "testnet", provider, signer });
const solana = new Solana({ network: "testnet", provider, signer });

// Initialize RenJS and pass in the initialized chains.
const renJS = new RenJS("testnet").withChains(bitcoin, ethereum, solana);

Gateways and gateway transactions

The main flow of interacting with RenJS is to first create a gateway, which contains all the required information for moving a specific asset between chains, including a recipient address or contract, and then move the asset through the gateway as one or more gateway transactions.

A gateway transaction is a collection of three sub-transactions on different chains:

  1. The in input transaction will involve locking or burning funds on an origin chain.

  2. The renVM transaction is submitted to RenVM.

  3. The out output transaction will mint or release funds on the target chain.

The in transaction will usually be submitted by the user, either as a deposit to an address or as a call to a smart contract. The renVM transaction will then result in RenVM either generating the out transaction, or returning a signature that can be submitted by the user as part of the out transaction.

RenVM will wait for the in transaction to reach the required number of confirmations before the renVM transaction can be processed.

Example

As an example, moving BTC from Bitcoin to Ethereum will involve:

  1. A BTC deposit by the user to the gateway's associated gateway address.

  2. The RenVM transaction which will generate a signature.

  3. An Ethereum transaction by the user to submit the signature and mint renBTC.

In order to return the BTC back to Bitcoin, the three transactions will be:

  1. An Ethereum transaction by the user to burn the renBTC.

  2. The RenVM transaction to confirm the burn of the renBTC, which will then generate the third transaction:

  3. A BTC transfer from RenVM's custody to the address specified by the user.

Initializing a gateway involves specifying all of the details, including the asset and the origin and target chain:

// A gateway for moving BTC from Bitcoin to Ethereum.
const btcGateway = await renJS.gateway({
asset: "BTC", // or bitcoin.assets.BTC,
from: bitcoin.GatewayAddress(),
to: ethereum.Account(),
});
// A gateway for moving DAI (originally from Ethereum) from the user's
// Binance Smart Chain account to a different address on Fantom.
const daiGateway = await renJS.gateway({
asset: ethereum.assets.DAI,
from: bsc.Account(),
to: fantom.Address("0x123456..."),
});

Each chain has various ways of specifying where the assets should come from or where they should go - for example bitcoin.GatewayAddress and bitcoin.Address, ethereum.Account and ethereum.Contract, and so on. These are documented on the page for each chain.

After initializing the gateway, the next step will be to either display a gateway address, or, for web3 chains, to request the user to submit the in transaction through their browser-connected wallet (e.g. MetaMask for Ethereum, or Phantom for Solana):

// Print the gateway address
console.log(`\
Deposit BTC to the following address: ${btcGateway.gatewayAddress}\
`);
// Submit the input transaction. This will prompt the user to sign
// a transaction, such as through MetaMask for Ethereum or other
// EVM chains.
daiGateway.in.submit();

Note that some chains require additional setup transactions to be submitted before the input transaction can be completed - see Setup Transactions.

tip

Chain transactions

Each of the in, renVM and out transactions are all instances of the TxWaiter or TxSubmitter interfaces, which follows the format of separating the submitting and the waiting for confirmations into two methods. When a transaction is generated outside of RenJS (e.g. a BTC deposit to a gateway address), the transaction will only have a .wait() method which will only return once the transaction has sufficient confirmations. When a transaction is being created through RenJS, it will also have a .submit() method which will create and submit the transaction.

These interfaces can be found here: TxWaiter and TxSubmitter

The next step is to handle any deposits that are received at the gateway address, or any burn or lock events detected in the in transaction. Each deposit or event will create a new gateway transaction, described earlier.

gateway.on("transaction", (tx) => {
// Wait for the `in` transaction to have enough confirmations.
await tx.in.wait();

// Submit the transaction to RenVM, and wait for it to be confirmed.
await tx.renVM.submit();
await tx.renVM.wait();

// Check if the user needs to submit the output transaction - it may have
// already been submitted by RenVM.
if (tx.out.submit) {
await tx.out.submit();
}
// Wait for the output transaction to be confirmed.
await tx.out.wait();
});