Web3.js is one of the most widely used JavaScript libraries for interacting with the Ethereum blockchain. You can create a Web3 instance with Rivet as a provider using:

var Web3 = require('web3');
var web3 = new Web3('https://YourApiKey.eth.rpc.rivet.cloud/');

From there, you can use the web3 object as documented to pull data from Rivet.