Lesson 8 : Explain this code (listenForTransactionMine).

[ameeetgaikwad]

What is the significance of this code, please explain in detail.

function listenForTransactionMine(transactionResponse, provider) {
    console.log(`Mining ${transactionResponse.hash}...`);
    return new Promise((resolve, reject) => {
        provider.once(transactionResponse.hash, (transactionReceipt) => {
            console.log(
                `Completed with ${transactionReceipt.confirmations} confirmations. `
            );
            resolve();
        });
    });
}

This function is used in :

async function withdraw() {
    if (typeof window.ethereum !== "undefined") {
        console.log("Withdrawing...");
        const provider = new ethers.providers.Web3Provider(window.ethereum);
        const signer = provider.getSigner();
        const contract = new ethers.Contract(contractAddress, abi, signer);
        try {
            const transactionResponse = await contract.withdraw();
            await listenForTransactionMine(transactionResponse, provider);
            console.log("Done!");
        } catch (error) {
            console.log(error);
        }
    }
}

Is it same as doing this? :

 const transactionResponse = await contract.withdraw();
const transactionReceipt=await transactionResponse.wait(1);

[krakxn]

Refer to #2140 (comment)

[ameeetgaikwad]

Ok. Can you ans the last line?

[krakxn]

No, it is not.

As provider.once is an event-listener (everytime the event is emitted), whereas in the latter you are just making a transaction for withdrawal and just mining that block.

[ameeetgaikwad]

@alymurtazamemon Help!

[alymurtazamemon]

@ameeetgaikwad It is not the same as the last lines, but the purpose is similar. Patrick created this function so he can reuse it in multiple places. It is taking the web3 provider as a parameter and a transaction response and uses the once method of that provider that will call once the first given parameter will be completed (that is our transaction response hash).

The whole function is telling the web3 provider, please wait for this transaction to complete and once it gets completed you can provide us the result of that transaction and move back to calling location so we can perform other things.

[ameeetgaikwad]

Ok Thank you!