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Plasma Bridge

Please check the latest Matic.js documentation on Plasma to get started.

A bridge is basically a set of contracts that help in moving assets from the root chain to the child chain. There are primarily two bridges to move assets between Ethereum and Polygon. First one is the Plasma bridge and the second one is called the PoS Bridge or Proof of Stake bridge. Plasma bridge provides increased security guarantees due to the Plasma exit mechanism.

However, there are certain restrictions on the child token and there is a 7-day withdrawal period associated with all exits/withdraws from Polygon to Ethereum on the Plasma bridge. The PoS Bridge is more flexible and features faster withdrawals.

This tutorial will act as a step-by-step guide to understand and use Plasma bridge using Matic JS, which is the easiest way to interact with the Plasma Bridge on Polygon Network.

Assets flow in Plasma Bridge​

We will be showcasing the flow for asset transfers on Polygon in this tutorial and how you can do the same using Matic.js:

  1. User deposits crypto assets in Polygon contract on main chain
  2. Once deposited tokens get confirmed on the main chain, the corresponding tokens will get reflected on the Polygon chain
    • The user can now transfer tokens to anyone they want instantly with negligible fees. Polygon chain has faster blocks (approximately 1 second). That way, the transfer will be done almost instantly.
  3. Once a user is ready, they can withdraw remaining tokens from the main chain. Withdrawal of funds is initiated from the Plasma Sidechain. A checkpoint interval of 5 mins is set, where all the blocks on the Polygon block layer are validated since the last checkpoint.
  4. Once the checkpoint is submitted to the main chain Ethereum contract, an Exit NFT (ERC721) token is created of equivalent value.
  5. The withdrawn funds can be claimed back to your Ethereum acccount from the main chain contract using a process-exit procedure.
    • User can also get a fast exit via 0x or Dharma (coming soon!)

Prerequisites:​

npm i @maticnetwork/maticjs-plasma

import { PlasmaClient } from "@maticnetwork/maticjs-plasma"

const plasmaClient = new PlasmaClient();

await plasmaClient.init({
    network: <network name>,  // 'testnet' or 'mainnet'
    version: <network version>, // 'mumbai' or 'v1'
    parent: {
      provider: <parent provider>,
      defaultConfig: {
            from: <from address>
      }
    },
    child: {
      provider: <child provider>,
      defaultConfig: {
            from: <from address>
      }
    }
});

Görli Faucet​

In order to make any transactions, you will also need some Ether in the test accounts that you will use while following the tutorial. In case you don’t have any ETH on Görli, you can use the faucet links given here — https://goerli-faucet.slock.it/.

Polygon Faucet​

Throughout this tutorial, we will be using the ERC20 token TEST on the Görli network as an example. This is a TEST token. In your DApp, you can replace it with any ERC20 token. To get some Test TEST tokens on Polygon Network, you can access the Polygon Faucet.

note

To use your own tokens for deposits and withdrawals, you'll have to get the token 'mapped', which essentially means making the contracts on main chain and sidechain 'aware' of your custom token.

Basic setup for the MetaMask Wallet (Optional)​

  1. Create a wallet: If you are new to wallets, then set up a MetaMask Account.
  2. Configure the Polygon testnet: To easily visualise the flow of funds on Polygon, it is instructive if you configure the Polygon testnet on Metamask. Note that we are using MetaMask here solely for visualization purposes. There is no requirement to use MetaMask at all for using Polygon.
  3. Create Multiple Accounts: Before starting with the tutorial, go ahead and have 3 Ethereum test accounts ready.
  4. Configure token on Polygon: In order to view the flow of funds easily on Polygon using Matic.js, you can configure tokens on Metamask. The TEST token, taken as an example for this tutorial, can be configured in MetaMask so as to easily visualize account balances. Again note this is optional. You can very easily query the token balances and other variables using web3.js