Introducing Web3

Web3 is a JavaScript library that can be used to communicate with an Ethereum node via RPC communication. Web3 works by exposing methods that have been enabled over RPC. This allows the development of user interfaces that make use of the web3 library in order to interact with the contracts deployed over the blockchain.

In order to expose the methods via geth, the following command can be used:

$ geth --datadir .ethereum/privatenet/ --networkid 786 --rpc --rpcapi 'web3,eth,debug' --rpcport 8001 --rpccorsdomain 'http://localhost:7777'

Note the --rpcapi flag that allows the web3, eth and debug methods.

This is a powerful library and can be explored further by attaching a geth instance. Later in the section, you will be introduced to the concepts and techniques of making use of web3 via JavaScript/HTML frontends.

The geth instance can be attached using the following command:

$ geth attach ipc:.ethereum/privatenet/geth.ipc

Once the geth JavaScript console is running...