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Smart Contracts

Read from and write to smart contracts on EVM-compatible chains.

Reading Contract State​

Programmatic​

import { erc20Abi } from "@fluxkitdev/onchain";

// Read a single value
const name = await app.onchain.contracts.read({
  address: "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48",
  abi: erc20Abi,
  method: "name",
  chain: "ethereum",
});
// => "USD Coin"

// Read with arguments
const balance = await app.onchain.contracts.read({
  address: "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48",
  abi: erc20Abi,
  method: "balanceOf",
  args: ["0x1234...5678"],
  chain: "ethereum",
});
// => 1000000000n (BigInt, 1000 USDC)

REST API​

curl -X POST http://localhost:3000/onchain/contracts/read \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer eyJhbGci..." \
  -d '{
    "address": "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48",
    "abi": "erc20",
    "method": "balanceOf",
    "args": ["0x1234...5678"],
    "chain": "ethereum"
  }'

Response (200):

{
  "result": "1000000000",
  "method": "balanceOf",
  "address": "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48"
}

Writing to Contracts​

Programmatic​

const tx = await app.onchain.contracts.write({
  address: "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48",
  abi: erc20Abi,
  method: "transfer",
  args: ["0xrecipient...", 1000000n], // 1 USDC
  chain: "ethereum",
  walletId: "65a1b2c3...", // Wallet to sign with
});

console.log(tx.hash);   // Transaction hash
console.log(tx.status); // "pending"

REST API​

curl -X POST http://localhost:3000/onchain/contracts/write \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer eyJhbGci..." \
  -d '{
    "address": "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48",
    "abi": "erc20",
    "method": "transfer",
    "args": ["0xrecipient...", "1000000"],
    "chain": "ethereum",
    "walletId": "65a1b2c3d4e5f6a7b8c9d0e1"
  }'

Response (200):

{
  "hash": "0xabc123...",
  "status": "pending",
  "chain": "ethereum"
}

Built-in ABIs​

FluxKit includes commonly used ABIs:

import {
  erc20Abi,
  erc721Abi,
  erc1155Abi,
} from "@fluxkitdev/onchain";

Or pass "erc20", "erc721", or "erc1155" as the abi field in REST requests.

Custom ABI​

const abi = [
  {
    name: "getValue",
    type: "function",
    stateMutability: "view",
    inputs: [],
    outputs: [{ type: "uint256" }],
  },
];

const value = await app.onchain.contracts.read({
  address: "0xcontract...",
  abi,
  method: "getValue",
  chain: "ethereum",
});

Contract Events​

Listen for contract events:

app.onchain.contracts.on({
  address: "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48",
  abi: erc20Abi,
  event: "Transfer",
  chain: "ethereum",
  handler: async (from, to, value, log) => {
    console.log(`Transfer: ${from} -> ${to}: ${value}`);
  },
});

Gas Estimation​

const gas = await app.onchain.contracts.estimateGas({
  address: "0xcontract...",
  abi: erc20Abi,
  method: "transfer",
  args: ["0xrecipient...", 1000000n],
  chain: "ethereum",
});

console.log(gas.gasLimit);  // Estimated gas units
console.log(gas.gasPrice);  // Current gas price
console.log(gas.totalCost); // Total cost in ETH