Metamask: Cannot use «window.ethereum» in Angular

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Metamask Error: Cannot use “window.ethereum” in Angular

When building an Ethereum-based application, MetaMask is one of the most important libraries for interacting with the Ethereum blockchain. However, when using Angular, developers often encounter an error that hampers their progress: Cannot use “window.ethereum”. In this article, we will look at the causes of this problem and provide a step-by-step solution to fix it.

The Problem

Developed by Coinbase, MetaMask is a popular browser extension for Ethereum wallets. It allows users to interact with the blockchain without leaving their web browser. To integrate MetaMask into an Angular application, developers rely on “window.ethereum”, which provides a way to programmatically access the Ethereum blockchain.

However, when using Angular, this approach often fails due to compatibility issues or security concerns. The reason lies in the way different frameworks and libraries interact with the browser environment. In particular, Angular’s dependency injection system and its use of window variables can cause conflicts with MetaMask’s implementation.

The solution

To solve this problem, we need to change the way we access window.ethereum. One solution is to create a custom provider that wraps MetaMask’s functionality in a more compatible way. This approach involves creating a separate service or module that provides a secure way for Angular applications to interact with Ethereum.

Here is a sample implementation:

import { Injectable } from '@angular/core';
import { ethers } from 'ethers';
@Injectable({
providedIn: 'root'
})
export class MetaMaskProvider {
private ethereumProvider = new MetaMaskInpageProvider();
constructor() {
this.ethereumProvider.init();
}
get Ethereum(): ethers.Web3 {
return this.ethereumProvider;
}
}

By using the @Injectable decorator and creating a custom provider, we can access window.ethereum safely and without any compatibility issues.

Angular Configuration

To use MetaMaskProvider, you need to configure Angular to recognize the custom provider:

import { NgModule } from '@angular/core';
import { MetaMaskProvider } from './metamask.provider';
@NgModule({
provider: [
{
provide: MetaMaskInpageProvider,
useClass: MetaMaskProvider
}
]
})
export class AppModule {}

Conclusion

By understanding the underlying issues and implementing a custom solution, developers can overcome the window.ethereum error when using Angular with MetaMask. This approach not only solves the compatibility issue but also provides a more secure way to interact with the Ethereum blockchain.

Remember to always follow best practices when developing web applications, including adhering to the latest security measures and browser extensions. Happy coding!

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