Interact with a smart contract using Hardhat

Prerequisites

You should already have a Hardhat project set up, and have deployed your smart contract successfully. See the deploy a smart contract using Hardhat tutorial for how to do so.

Optionally, but strongly recommended: You should also have successfully verified your smart contract. See the verify a smart contract using Hardhat tutorial for how to do so.

Start the Hardhat console

Use the following command to start an interactive Javascript REPL.

npx hardhat console --network inj_testnet

Now the shell will be a NodeJs REPL instead of your regular shell (bash, zsh, et cetera). In this REPL, we will create an instance of the Counter smart contract. To do so, use ethers.getContractFactory(...) and contract.attach('0x...');. For example, if the smart contract was deployed to 0x98798cc92651B1876e9Cc91EcBcfe64cac720a1b, the commands should look like this:

const Counter = await ethers.getContractFactory('Counter');
const counter = await Counter.attach('0x98798cc92651B1876e9Cc91EcBcfe64cac720a1b');

Note that in this REPL, you will see > as the shell prompt. The results of each prompt are output without this prefix. The contents of your terminal will therefore look similar to this:

> const Counter = await ethers.getContractFactory('Counter');
undefined
> const counter = await Counter.attach('0x98798cc92651B1876e9Cc91EcBcfe64cac720a1b');
undefined

Now you can interact with the smart contract using counter.

Invoke function - query

Queries are read-only operations. So smart contract state is not updated. As no state change is needed, no wallets, signatures, or transaction fees (gas) are required.

Use the following command to query the value() function.

await counter.value();

This should output the following.

0n

Note that 0n means 0, the n suffix indicates that it is a BigInt and not a Number.

This is because Solidity’s uint256 (the return type of the value() function in the smart contract), is not possible to be represented with Number, as the largest possible integer value for that is 2^53 - 1. Thus BigInt needs to be used instead.

Invoke function - transaction

Transactions are write operations. So smart contract state is updated. As state change can occur, the transaction must be signed by a wallet, and transaction fees (gas) need to be paid.

Use the following command to transact the increment(num) function.

await counter.increment(1, { gasPrice: 160e6, gasLimit: 2e6 });

Note that gas price is stated in wei. 1 wei = 10^-18 INJ.

If successful, this should produce a result similar to the following:

ContractTransactionResponse { ...

After updating the state, you can query the new state. The result will reflect the state change.

await counter.value();

This time the result should be 1n because 0 + 1 = 1.

1n

Stop the Hardhat console

Press Ctrl+C twice in a row, or enter the .exit command.

Next steps

Congratulations, you have completed this entire guide for developing EVM smart contracts on Injective using Hardhat!

Smart contracts do not provide a user experience for non-technical users. To cater to them, you will need to build a decentralised application. To do so, check out the your first dApp guides!