Detect MetaMask

The presence of the MetaMask Ethereum provider object, window.ethereum, in a user's browser indicates an Ethereum user.

To demonstrate this, verify if your browser is running MetaMask by copying and pasting the following code snippet in the developer console of your browser:

if (typeof window.ethereum !== 'undefined') {
  console.log('MetaMask is installed!');
}

tip

To differentiate MetaMask from other Ethereum-compatible browsers, you can detect MetaMask using the window.ethereum.isMetaMask property.

Use @metamask/detect-provider

We recommend using the @metamask/detect-provider module to detect the MetaMask Ethereum provider on any platform or browser.

Use npm to install @metamask/detect-provider in your project directory:

npm i @metamask/detect-provider

In the example project script, the following code detects the provider using @metamask/detect-provider:

index.js

// This function detects most providers injected at window.ethereum.
import detectEthereumProvider from '@metamask/detect-provider';

// This returns the provider, or null if it wasn't detected.
const provider = await detectEthereumProvider();

if (provider) {
  // From now on, this should always be true:
  // provider === window.ethereum
  startApp(provider); // initialize your app
} else {
  console.log('Please install MetaMask!');
}

function startApp(provider) {
  // If the provider returned by detectEthereumProvider isn't the same as
  // window.ethereum, something is overwriting it – perhaps another wallet.
  if (provider !== window.ethereum) {
    console.error('Do you have multiple wallets installed?');
  }
  // Access the decentralized web!
}

Compile the module

Use a bundler such as Webpack to compile the module and create an output script. Install Webpack in your project directory:

npm i --save-dev webpack

Install the Webpack CLI:

npm i --save-dev webpack-cli

Compile the module:

npx webpack

note

When compiling the module, you might need to pass CLI options such as --experiments-top-level-await. You can alternatively specify options in a configuration file as follows:

webpack.config.cjs

module.exports = {
    experiments: {
        topLevelAwait: true,
    },
};

Run npx webpack again upon any changes to index.js. See Webpack's Getting Started guide for more information.