web3.js provides us with JavaScript APIs to communicate with geth. It uses JSON-RPC internally to communicate with geth. web3.js can also communicate with any other kind of Ethereum node that supports JSON-RPC. It exposes all JSON-RPC APIs as JavaScript APIs; that is, it doesn't just support all the Ethereum-related APIs; it also supports APIs related to Whisper and Swarm.
You will learn more and more about web3.js as we build various projects, but for now, let's go through some of the most used APIs of web3.js and then we will build a frontend for our ownership smart contract using web3.js.
At the time of writing this, the latest version of web3.js is 0.16.0. We will learn everything with respect to this version.
web3.js is hosted at https://github.com/ethereum/web3.js and the complete documentation is hosted at https://github.com/ethereum/wiki/wiki/JavaScript-API.
...
