2.0.0 • Public • Published


MetaMask's legacy window.web3.


MetaMask strongly recommends that you read our migration guide before using this package. You should only rely on this package if you need a temporary fix or are no longer actively developing your web3 site.

In the near future, MetaMask will stop injecting window.web3 into web pages. When we do this, if your website relies on MetaMask's window.web3 to function, it will break on that date unless you take action. Please refer to the original announcement if you want to know why we're doing this.

If you do not wish to take either of the recommended migration paths, we provide this library as a drop-in replacement for our injected window.web3. Simply add it to your site using one of the methods outlined below, and your Ethereum functionality will continue to work after we stop injecting window.web3.

You can add this package before we stop injecting window.web3, without disrupting the Ethereum functionality of your website.


This package is designed to emulate the functionality of our injected window.web3. That said, we do not guarantee complete functional parity, and you may have to fix some bugs yourself. We also make no guarantees about future maintenance of this package, and it is unlikely to support any new features added to the MetaMask provider API.


As a <script> in your web page:

    <!-- The legacy-web3 script must run BEFORE your other scripts. -->
    <script src="https://unpkg.com/@metamask/legacy-web3@latest/dist/metamask.web3.min.js"></script>
    <!-- Or: -->
    <script src="https://unpkg.com/@metamask/legacy-web3@latest/dist/metamask.web3.js"></script>

Or add as a Node dependency:

yarn add @metamask/legacy-web3

# or

npm install @metamask/legacy-web3
import '@metamask/legacy-web3'

// or


const { web3 } = window
const selectedAddress = web3.eth.defaultAccount

Initialization Criteria

This package will only initialize window.web3 under the following circumstances:

  • It detects an existing window.ethereum
  • It does not detect an existing window.web3

window.ethereum.isMetaMask can be true or falsy. If it is falsy and there is no existing window.web3, this package will initialize its window.web3, but there are no guarantees that it will work with non-MetaMask providers.




npm i @metamask/legacy-web3

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