Metamask: ReferenceError: Buffer is not defined

Understanding MetaMask Sign Typed Data Login

As a digital asset enthusiast, you’re likely familiar with Metamask, the popular wallet app that enables seamless interactions between your Ethereum accounts and decentralized applications (dApps). One of the exciting features of Metamask is its ability to handle signedTypedData login using Web3.js. However, I’d like to take this opportunity to dive deeper into a common issue that can arise when implementing MetaMask’s sign Typed Data login: the Buffer not defined error.

The Issue

When you try to verify signedTypedData with Metamask, it expects a Buffer object as input. This is because the eth.util.signTypedData() function returns an Ethereum transaction hash in the format of a hexadecimal string (e.g., “0x…”).

However, when you’re working with typed data or other types that don’t conform to the Buffer interface, like signedTypedData, Metamask throws an error. Specifically, it raises a ReferenceError because Buffer is not defined.

The Solution

To resolve this issue, you’ll need to ensure that your typed data conforms to the Buffer interface. Here are a few approaches:

• Define the type of your typed data: If possible, define the exact type of your signedTypedData in the Buffer object. You can use TypeScript or JavaScript’s built-in types to specify this.

import * as Web3 from 'web3';


const typedData = {

  // your typed data here,

  type: Buffer.from('your-type-here'),

  value: 'your-value-here',

};


const transactionHash = web3.eth.util.signTypedData(typedData);

• Use a polyfill: If you’re working with older browsers or Node.js versions without support for TypedArrays, consider using a polyfill like typedarray-buffer or typedarray-polyfill. These libraries provide a fallback implementation of the Buffer interface.

const { Buffer } = require('buffer');


const typedData = {

  type: 'Buffer',

  value: Buffer.from('your-type-here'),

};


const transactionHash = web3.eth.util.signTypedData(typedData);

Conclusion

Implementing MetaMask’s sign Typed Data login requires some care when working with typed data. By following the tips outlined above, you should be able to resolve the Buffer not defined error and successfully verify signedTypedData with your app.

Remember to always check the official documentation for each library or API you’re using, as their behavior may change over time. Happy coding!