Getting Started with the OVM: Simple ERC20 Token Tutorial

Hi there! Welcome to our OVM ERC20 tutorial.

If you're interested in writing your first L2-compatible smart contract, you've come to the right place! This tutorial will cover how to move an existing contract and its tests into the wonderful world of L2.

Set up

To start out, clone this example repo as a starting point.

git clone https://github.com/ethereum-optimism/ERC20-Example.git

Now, enter the repository

cd ERC20-Example

Install all dependencies

yarn install

This project represents a fresh, non-OVM ERC20 contract example. Feel free to stop here and have a quick look at the contract and tests.

In this tutorial, we'll cover the steps required to bring it into the world of L2. First, let's make sure all of our tests are running in our normal Ethereum environment: 

yarn test

You should see all of the tests passing. We're now ready to convert the project to build and test in an OVM environment!

Configuring the Transpiler

First, we need to configure ethereum-waffle (which is an alternative to truffle) to use our new transpiler-enabled Solidity compiler. To do this, edit the waffle-config.json and replace it with:

{
  "sourcesPath": "./contracts",
  "targetPath": "./build",
  "npmPath": "./node_modules",
  "solcVersion": "./node_modules/@eth-optimism/solc-transpiler",
  "compilerOptions": {
    "outputSelection": {
      "*": {
        "*": ["*"]
      }
    },
    "executionManagerAddress": "0xA193E42526F1FEA8C99AF609dcEabf30C1c29fAA"
  }
}

Using the Full Node

To use the OVM to run our tests, open the test file at test/erc20.spec.js. We can import the OVM-ified versions of getWallets, createMockProvider, and deployContract near the top of the test file:

const { createMockProvider, getWallets, deployContract } = require('@eth-optimism/rollup-full-node')

Now remove the duplicated imports from ethereum-waffle, replacing the import on Line 2 with:

const {solidity} = require('ethereum-waffle');

Our imports at the top of the file should now look like: 

const {use, expect} = require('chai');
const {solidity} = require('ethereum-waffle');
const {createMockProvider, getWallets, deployContract } = require('@eth-optimism/rollup-full-node')
const ERC20 = require('../build/ERC20.json');

We're almost there! After we've run our tests on the OVM, we need to stop our OVM server. We're going to add a single line of code after our before() hook in order to close our OVM Server after our tests run:

  before(async () => {
    ...
  })

  //ADD THIS
  after(() => {provider.closeOVM()})

Running the New Tests

Great, we're ready to go! Now you can try to re-run your tests on top of the OVM with

yarn test

Wasn't that easy?

The OVM provides a fresh new take on layer 2 development: it's identical to layer 1 development. No hoops, no tricks--the Ethereum you know and love, ready to scale up with L2. For more info on our progress and what's going on behind the scenes, you can follow us on Twitter and check out our docs!

Troubleshooting

Not working for you? It might help to check out this easy to read Diff to show you exactly which lines you should be altering. You can also check out the final working codebase that we have added to a seperate branch here

Still not working? Create a Github Issue, or hop in our Discord channel and ask away.