0gfoundation/skills/chain/interact-contract

Interact with 0G Chain Contracts

Metadata

• Category: chain
• SDK: ethers ^6.13.0
• Activation Triggers: "call contract", "read contract", "interact", "write contract", "contract function"

Purpose

Read from and write to deployed smart contracts on 0G Chain using ethers v6. Covers view functions, state-changing transactions, event listening, and gas estimation.

Prerequisites

• Node.js >= 18
• ethers ^6.13.0 installed
• Contract ABI and address
• .env with PRIVATE_KEY, RPC_URL

Quick Workflow

Read (View Functions)

1. Create provider (no wallet needed for reads)
2. Create contract instance with ABI and address
3. Call view function

Write (State Changes)

1. Create provider and wallet
2. Create contract instance with wallet as signer
3. Call state-changing function
4. Wait for transaction confirmation

Core Rules

ALWAYS

• Use ethers v6 syntax throughout
• Use await contract.getAddress() (not contract.address)
• Use await contract.waitForDeployment() (not .deployed())
• Wait for transaction confirmation with tx.wait()
• Use native BigInt (not BigNumber)

NEVER

• Use ethers v5 patterns
• Skip transaction confirmation for important operations
• Hardcode contract addresses in source (use .env)

Code Examples

Read Contract State

import { ethers } from 'ethers';
import 'dotenv/config';

const ABI = [
  'function getValue() view returns (uint256)',
  'function balanceOf(address) view returns (uint256)',
  'function owner() view returns (address)',
];

async function readContract() {
  const provider = new ethers.JsonRpcProvider(process.env.RPC_URL);
  const contract = new ethers.Contract(process.env.CONTRACT_ADDRESS!, ABI, provider);

  const value = await contract.getValue();
  console.log('Value:', value.toString());

  const balance = await contract.balanceOf(process.env.WALLET_ADDRESS!);
  console.log('Balance:', ethers.formatEther(balance));

  const owner = await contract.owner();
  console.log('Owner:', owner);
}

Write to Contract

async function writeContract() {
  const provider = new ethers.JsonRpcProvider(process.env.RPC_URL);
  const wallet = new ethers.Wallet(process.env.PRIVATE_KEY!, provider);

  const ABI = [
    'function setValue(uint256) external',
    'function transfer(address, uint256) external returns (bool)',
  ];
  const contract = new ethers.Contract(process.env.CONTRACT_ADDRESS!, ABI, wallet);

  // Simple write
  const tx = await contract.setValue(42);
  const receipt = await tx.wait();
  console.log('Tx hash:', receipt.hash);
  console.log('Gas used:', receipt.gasUsed.toString());

  // Write with value
  const tx2 = await contract.transfer('0xRecipient...', ethers.parseEther('1.0'));
  await tx2.wait();
}

Listen for Events

async function listenForEvents() {
  const provider = new ethers.JsonRpcProvider(process.env.RPC_URL);
  const ABI = [
    'event Transfer(address indexed from, address indexed to, uint256 amount)',
    'event ValueChanged(uint256 newValue)',
  ];
  const contract = new ethers.Contract(process.env.CONTRACT_ADDRESS!, ABI, provider);

  // Real-time listener
  contract.on('ValueChanged', (newValue) => {
    console.log('Value changed to:', newValue.toString());
  });

  contract.on('Transfer', (from, to, amount) => {
    console.log(`Transfer: ${from} → ${to}: ${ethers.formatEther(amount)}`);
  });

  // Query past events
  const filter = contract.filters.Transfer();
  const events = await contract.queryFilter(filter, -1000); // Last 1000 blocks
  console.log(`Found ${events.length} transfer events`);
}

Gas Estimation

async function estimateGas() {
  const provider = new ethers.JsonRpcProvider(process.env.RPC_URL);
  const wallet = new ethers.Wallet(process.env.PRIVATE_KEY!, provider);

  const ABI = ['function setValue(uint256) external'];
  const contract = new ethers.Contract(process.env.CONTRACT_ADDRESS!, ABI, wallet);

  const gasEstimate = await contract.setValue.estimateGas(42);
  console.log('Estimated gas:', gasEstimate.toString());

  // Execute with gas buffer
  const tx = await contract.setValue(42, {
    gasLimit: (gasEstimate * 120n) / 100n, // 20% buffer
  });
  await tx.wait();
}

Using Full ABI (from compilation)

import * as fs from 'fs';

async function interactWithArtifact() {
  const artifact = JSON.parse(
    fs.readFileSync('./artifacts/contracts/MyContract.sol/MyContract.json', 'utf8'),
  );

  const provider = new ethers.JsonRpcProvider(process.env.RPC_URL);
  const wallet = new ethers.Wallet(process.env.PRIVATE_KEY!, provider);
  const contract = new ethers.Contract(process.env.CONTRACT_ADDRESS!, artifact.abi, wallet);

  // Now use any function from the contract
  const value = await contract.getValue();
  console.log('Value:', value.toString());
}

ethers v6 Quick Reference

| Operation | v5 (DO NOT USE) | v6 (CORRECT) | | ------------ | -------------------------------------- | ------------------------------------ | | Parse ether | ethers.utils.parseEther("1") | ethers.parseEther("1") | | Format ether | ethers.utils.formatEther(x) | ethers.formatEther(x) | | Big numbers | BigNumber.from(42) | 42n (native BigInt) | | Get address | contract.address | await contract.getAddress() | | Wait deploy | await contract.deployed() | await contract.waitForDeployment() | | Provider | new ethers.providers.JsonRpcProvider | new ethers.JsonRpcProvider |

Anti-Patterns

// BAD: ethers v5 patterns
const value = ethers.utils.parseEther('1.0'); // v5!
const provider = new ethers.providers.JsonRpcProvider(url); // v5!
const big = BigNumber.from(42); // v5!

// BAD: Not waiting for confirmation
await contract.setValue(42); // Fire and forget — bad!

// BAD: Hardcoded addresses
const contract = new ethers.Contract('0x123...', abi, wallet);

Common Errors & Fixes

| Error | Cause | Fix | | ----------------------- | ------------------------ | ------------------------------ | | execution reverted | Require/revert condition | Check function parameters | | insufficient funds | Wallet empty | Fund wallet | | nonce too low | Pending tx | Wait or set nonce manually | | cannot estimate gas | Function will revert | Check args and contract state | | call revert exception | View function reverted | Check function exists and args |

Related Skills

• Deploy Contract — deploy contracts first
• Scaffold Project — project setup
• Storage + Chain — on-chain + storage

References

• Chain Patterns
• Network Config
• ethers v6 Docs