The Reactive Network Basic Demo walks through the core Reactive pattern: a contract on an origin chain emits an event, Reactive detects it and automatically sends a callback to a contract on a destination chain. The destination contract doesn't contain any real business logic. It simply receives the callback, confirming that Reactive Network has performed its function successfully.

The demo focuses on two key behaviors. First, low-latency monitoring: Reactive watches for log events emitted by a contract on the origin chain. Second, conditional reacting: when a threshold is met (in this case, a transfer of at least 0.001 ETH), Reactive triggers a callback to the destination chain.

The setup is intentionally minimal. The same pattern applies to more complex scenarios like stop orders, cross-chain arbitrage, or decentralized algorithmic trading.

Origin Contract: BasicDemoL1Contract is the origin contract that accepts Ether, returns it to the sender, and emits a Received event containing the transaction origin, sender, and value. This event is what Reactive Network monitors.

Reactive Contract: BasicDemoReactiveContract is the Reactive contract, deployed on Reactive Network itself. On deployment, it subscribes to Received events from the origin contract. When an event arrives, the react() function checks whether the value (topic_3) meets a minimum threshold of 0.001 ETH. If it does, the contract emits a Callback event with a payload targeting the destination contract.

Destination Contract: BasicDemoL1Callback is the destination contract. It receives callbacks from Reactive Network, verifying that the caller is the authorized callback proxy, and emits a CallbackReceived event logging the transaction origin, sender, and Reactive sender addresses.

Before deploying, set the following environment variables:

• ORIGIN_RPC — RPC URL for the origin chain, (see Chainlist).
• ORIGIN_CHAIN_ID — ID of the origin chain (see Reactive Docs).
• ORIGIN_PRIVATE_KEY — Private key for signing transactions on the origin chain.
• DESTINATION_RPC — RPC URL for the destination chain, (see Chainlist).
• DESTINATION_CHAIN_ID — ID of the destination chain (see Reactive Docs).
• DESTINATION_PRIVATE_KEY — Private key for signing transactions on the destination chain.
• REACTIVE_RPC — RPC URL for Reactive Network (see Reactive Docs).
• REACTIVE_PRIVATE_KEY — Private key for signing transactions on Reactive Network.
• DESTINATION_CALLBACK_PROXY_ADDR — The callback proxy address on the destination chain (see Reactive Docs).

ℹ️ Reactive faucet on Ethereum Sepolia

To receive testnet REACT, send SepETH to the Reactive faucet on Ethereum Sepolia: 0x9b9BB25f1A81078C544C829c5EB7822d747Cf434. The exchange rate is 100 REACT per 1 SepETH. Do not send more than 5 SepETH in a single transaction as any excess is lost.

⚠️ Broadcast Error

If you see error: unexpected argument '--broadcast' found, your Foundry version does not support the --broadcast flag for forge create. Remove it from the command and re-run.

Deploy BasicDemoL1Contract and save the Deployed to address as ORIGIN_ADDR.

forge create --broadcast --rpc-url $ORIGIN_RPC --private-key $ORIGIN_PRIVATE_KEY src/demos/basic/BasicDemoL1Contract.sol:BasicDemoL1Contract

Deploy BasicDemoL1Callback and save the Deployed to address as CALLBACK_ADDR. This contract requires a small ETH deposit and takes the callback proxy address as a constructor argument.

forge create --broadcast --rpc-url $DESTINATION_RPC --private-key $DESTINATION_PRIVATE_KEY src/demos/basic/BasicDemoL1Callback.sol:BasicDemoL1Callback --value 0.02ether --constructor-args $DESTINATION_CALLBACK_PROXY_ADDR

Deploy BasicDemoReactiveContract, pointing it at the origin contract (ORIGIN_ADDR) on ORIGIN_CHAIN_ID and the destination contract (CALLBACK_ADDR) on DESTINATION_CHAIN_ID.

The topic_0 value 0x8cabf31d2b1b11ba52dbb302817a3c9c83e4b2a5194d35121ab1354d69f6a4cb corresponds to the Received event signature that the Reactive contract subscribes to.

forge create --broadcast --rpc-url $REACTIVE_RPC --private-key $REACTIVE_PRIVATE_KEY src/demos/basic/BasicDemoReactiveContract.sol:BasicDemoReactiveContract --value 0.1ether --constructor-args $ORIGIN_CHAIN_ID $DESTINATION_CHAIN_ID $ORIGIN_ADDR 0x8cabf31d2b1b11ba52dbb302817a3c9c83e4b2a5194d35121ab1354d69f6a4cb $CALLBACK_ADDR

Send at least 0.001 ETH to the origin contract. This triggers the Received event, which the Reactive contract picks up and forwards as a callback to the destination chain.

cast send $ORIGIN_ADDR --rpc-url $ORIGIN_RPC --private-key $ORIGIN_PRIVATE_KEY --value 0.001ether

Once the transaction confirms, Reactive Network will initiate a callback transaction to CALLBACK_ADDR. You can verify it by checking the destination contract's events on Etherscan like shown here.