Track 6 · dApps & frontend · lesson 2

Reading state with viem

11 min

You have been using viem all along — the Forge's tests are written in it. Now you point it at a real network instead of the in-browser chain.

A public client

import { createPublicClient, http, formatEther } from "viem";
import { mainnet } from "viem/chains";

const client = createPublicClient({
  chain: mainnet,
  transport: http("https://rpc.example.com"),
});

const balance = await client.getBalance({ address: "0xf39f…2266" });
console.log(formatEther(balance), "ETH");   // wei -> a human number

formatEther turns the raw wei integer into a readable decimal — the display step from track 5, applied. Its opposite, parseEther("1.5"), turns a human number back into wei for sending.

Reading a contract

const symbol = await client.readContract({
  address: tokenAddress,
  abi: erc20Abi,
  functionName: "symbol",
});

const balance = await client.readContract({
  address: tokenAddress,
  abi: erc20Abi,
  functionName: "balanceOf",
  args: [userAddress],
});

The abi is how viem knows how to encode the call and decode the answer — the exact role it played in the Forge's test runner. Reads cost no gas and need no wallet.

Multicall

Reading twenty balances as twenty separate requests is slow. viem's multicall batches them into one RPC round-trip:

const results = await client.multicall({
  contracts: addresses.map((a) => ({
    address: token, abi: erc20Abi, functionName: "balanceOf", args: [a],
  })),
});

One request, twenty answers. This is the difference between a portfolio page that loads instantly and one that spinners for five seconds.