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Set up your development environment

You can easily set up a simple dapp to integrate with MetaMask.

Prerequisites​

  • MetaMask installed in the browser of your choice on your development machine. We recommend running a development network on MetaMask when developing a dapp.

  • A text editor of your choice, such as VS Code. You can install the Live Server extension for VS Code to easily launch a local development server for your dapp.

  • A module bundler, such as Webpack.

  • npm.

Set up a new project​

Create a project directory with the following structure:

simple-dapp/
├─ src/
│  ├─ index.js
├─ dist/
│  ├─ index.html

For any Ethereum dapp to work, your project script index.js must:

important

If you import any modules into your project, such as @metamask/detect-provider, use a bundler such as Webpack to compile the modules and create an output script dist/main.js. See Webpack's Getting Started guide for more information.

tip

We also recommend importing MetaMask SDK to enable a reliable, secure, and seamless connection from your dapp to a MetaMask wallet client.

Example​

The following is an example simple dapp script and HTML file:

index.js
/*****************************************/
/* Detect the MetaMask Ethereum provider */
/*****************************************/

import detectEthereumProvider from '@metamask/detect-provider';

const provider = await detectEthereumProvider();

if (provider) {
  startApp(provider);
} else {
  console.log('Please install MetaMask!');
}

function startApp(provider) {
  if (provider !== window.ethereum) {
    console.error('Do you have multiple wallets installed?');
  }
}

/**********************************************************/
/* Handle chain (network) and chainChanged (per EIP-1193) */
/**********************************************************/

const chainId = await window.ethereum.request({ method: 'eth_chainId' });

window.ethereum.on('chainChanged', handleChainChanged);

function handleChainChanged(chainId) {
  window.location.reload();
}

/***********************************************************/
/* Handle user accounts and accountsChanged (per EIP-1193) */
/***********************************************************/

let currentAccount = null;
window.ethereum.request({ method: 'eth_accounts' })
  .then(handleAccountsChanged)
  .catch((err) => {
    console.error(err);
  });

window.ethereum.on('accountsChanged', handleAccountsChanged);

function handleAccountsChanged(accounts) {
  if (accounts.length === 0) {
    console.log('Please connect to MetaMask.');
  } else if (accounts[0] !== currentAccount) {
    currentAccount = accounts[0];
    showAccount.innerHTML = currentAccount;
  }
}

/*********************************************/
/* Access the user's accounts (per EIP-1102) */
/*********************************************/

const ethereumButton = document.querySelector('.enableEthereumButton');
const showAccount = document.querySelector('.showAccount');

ethereumButton.addEventListener('click', () => {
  getAccount();
});

async function getAccount() {
  const accounts = await window.ethereum.request({ method: 'eth_requestAccounts' })
    .catch((err) => {
      if (err.code === 4001) {
        console.log('Please connect to MetaMask.');
      } else {
        console.error(err);
      }
    });
  const account = accounts[0];
  showAccount.innerHTML = account;
}