About the Project
Polkadot.js is a very simple scaffolding browser extension that injects a Polkadot API Signer into a page, along with any associated accounts, allowing for use by any DApp. The extension only does one thing: it manages accounts and allows the signing of transactions with those accounts. It does not inject providers for use by DApps at this early point, nor does it perform wallet functions e.g., sending funds.
About the Integration
Moonbeam is an Ethereum-compatible Substrate-based network, which means it can be used with both EVM and Substrate-based block explorers. You can use Polkadot.js to view and interact with the Substrate layer of Moonbase Alpha or a local Moonbeam node.
The Polkadot.js app uses the WebSocket endpoint to interact with the Moonbeam network. To connect it to a standalone Moonbeam node, you can follow the steps in this tutorial.