Lesson 13 Await vs wait()

[Nlferu]

Hello everyone,

I'm on Lesson 13 and I need simple explanation regarding await and wait(1). I know that we are using wait() to wait for block to be generated, and performing transaction as below:

const approveTx = await erc20.approve(spender, amount)
await approveTx.wait(1)

Is totally clear, but why in our aaveBorrow.js we are performing below transaction only with await keyword like below examples:

await approveERC20(AMOUNT, lendingPool.address, wethAddress, deployer)
await lendingPool.deposit(wethAddress, AMOUNT, deployer, 0)
await borrowDai(networkConfig[network.config.chainId].daiToken, lendingPool, amountDaiToBorrowWei, deployer)

And last question is regarding missing const for below txResponse, why it is not throwing error that it's undefined? It is located in our approveErc20 function.

txResponse = await erc20Token.approve(spenderAddress, amount)
await txResponse.wait(1)

[alymurtazamemon]

@Neftyr

wait we use with transactions which wait for the number of block confirmations we specified in it.

await we use in front of function calls which perform asynchronous calls inside. This allows the function to complete before our code moves down the line.

And about the const, this variable must be defined somewhere before use.

[rajanlagah]

@alymurtazamemon can you check before answering? Sorry to be rude, but jumping to answer everything without proper research and knowledge will do no good. Just so you know, only ans if you know. I hope you will understand

@Neftyr regarding your question

And last question is regarding missing const for below txResponse, why it is not throwing error that it's undefined? It is located in our approveErc20 function.

I saw it is not defined elsewhere. And why its not throwing errors? Because In js if you define a variable and assign value at the same time it becomes a global variable.
so

 newVar = "some value" // is fine in js 

now newVar is a global variable.

[alymurtazamemon]

@Neftyr As you can see below it is better to wait for the confirmation of a transaction before proceeding further so we can perform other tasks on the updated data on the blockchain.

[Nlferu]

Hello @rajanlagah

Thank you, soo much for simple clarification!

@alymurtazamemon regarding wait(1), as I can see it makes no difference and it pops immediately after real waiting is happening. I have marked slowdown in console with red underline. Code is running with slowdown in the same place regardless we have wait(1) or not.

Code without wait. Console is slowing down as showed below after printing Depositing Collateral....

    // Deposit
    console.log("Depositing Collateral...")
    await lendingPool.deposit(wethAddress, AMOUNT, deployer, 0)
    console.log("Collateral Deposited!")

Code with wait. Console is slowing down in same place after printing Depositing Collateral....

    // Deposit
    console.log("Depositing Collateral...")
    const slow = await lendingPool.deposit(wethAddress, AMOUNT, deployer, 0)
    console.log("waiting...")
    await slow.wait(1)
    console.log("Collateral Deposited!")

In this case I believe that wait is useless here for real, but I still wonder why as we are using it in approveERC20() function for example in course updated repo. I can also confirm that for python we had to use wait() after every single transaction because otherwise maybe code would run correct but at the end it would throw error/warning anyway because amount of blocks was not correct and JS does not throw such errors/warnings.

[alymurtazamemon]

@Neftyr It is waiting at this point because lendingPool.deposit function is asynchronous and we are adding await before it so it can complete its execution. After the execution completion, it will trigger a transaction, so now it is up to you whether you want to wait for the transaction block confirmations. Here it is a hardhat network which is why it is so fast, on the testnet or mainnet networks it is recommended to have at least wait for 6 block confirmations.

You are getting confused with the wait for code completion and the wait for block confirmations.

Let me give you an example;

Suppose you have a function which performs some delay like this;

function timeout(delay: number) {
    return new Promise((res) => setTimeout(res, delay));
}

await timeout(5000);
console.log("Timeout completed");

Now here while calling this function I am adding a value of 5000 which is equal to 5 sec. So when you run this code the program will stop here for 5 seconds before printing "Timeout completed"; This is called wait for code completion. Here we are waiting for the timeout function to complete before we go further.

But in blockchains, we also have TransactionResponses (of type ContractTransaction) which functions returns and in order to confirm that our transaction is added to the blockchain we wait for this transaction response further.

It is another discussion about why we wait for transaction responses which I have answered many times hope you will find it in the discussions. If not just continue and you will experience this.

[Nlferu]

Hello @alymurtazamemon

Ok I think I got it now, thank you for explanation. So to sum up we should always be using wait(x), (x = blocks amount) after every single transaction like we do in python as await only waits for function to be completed and not for block to be added to blockchain. I'm always following repo code as it is most up to date and without bugs mostly, but this one clearly made me confused. Thanks again for clarification on this!