Lesson 14: How come localhost has a subscriptionId?

[DorianDaSilva]

I am going through lesson 14 and noticed that helper file includes a subId for VRF coordinator but I thought that we had to simulate vrf when on localnetwork aka hardhat.

Is that subscriptionId serving any purpose when assigned to local network?

[alymurtazamemon]

@DorianDaSilva Yes, I will be needed for the testnet when we deploy the script for random nft

[DorianDaSilva]

@alymurtazamemon I understand we will be using the subId for kovan or goerli but what about hardhat (localhost) ? I see it in the helper file with a subId number, that one is irrelevant and won't be used, correct?

[alymurtazamemon]

@DorianDaSilva Yes!, we will mock for it.

[krakxn]

We are using the Mock when we are on a local network (e.g. localhost), as so (an example to illustrate):

if (chainId == 31337) {
        // Create VRFV2 Subscription
        const vrfCoordinatorV2Mock = await ethers.getContract("VRFCoordinatorV2Mock")
        vrfCoordinatorV2Address = vrfCoordinatorV2Mock.address
        const transactionResponse = await vrfCoordinatorV2Mock.createSubscription()
        const transactionReceipt = await transactionResponse.wait()
        subscriptionId = transactionReceipt.events[0].args.subId
        
        // Fund the subscription
        // Our mock makes it so we don't actually have to worry about sending fund
        await vrfCoordinatorV2Mock.fundSubscription(subscriptionId, FUND_AMOUNT)
    }

[DorianDaSilva]

Thank you!