Web3.eth.getGasPrice not working on zkSync?

Question

I m trying to estimate what is current gas price with Web3.js library on zkSync layer2 network however I m constantly getting same result: 250000000 for multiple days so I assume it s not working correctly. Is web3.js not working with zkSync? https://web3js.readthedocs.io/en/v1.10.0/web3-eth.html?highlight=getGasPrice#getgasprice

const Web3 = require("web3"); // Web3 library
const web3 = new Web3("https://mainnet.era.zksync.io");
let gasPrice = await web3.eth.getGasPrice();

Answer 1

getGasPrice() returns the median gas price (calculated from previous few blocks). https://web3js.readthedocs.io/en/v1.2.11/web3-eth.html#getgasprice

You can retrieve that by:

const result = await web3.eth.getGasPrice()
console.log(web3.utils.fromWei(result, 'ether'))

As to why its 250000000, that's because that's the baseFeePerGas set: https://github.com/matter-labs/foundry-zksync#get-latest-block

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If you want to estimate the gas price for a transaction you want to make, you can use the estimateGas function. https://web3js.readthedocs.io/en/v1.2.11/web3-eth.html#estimategas

You can do something like:

const gasAmount = await web3.eth.estimateGas({
    to: toAddress,
    from: fromAddress,
    value: web3.utils.toWei(`${amount}`, 'ether'),
})

The input to estimateGas function is a transaction object.

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To add a bit further to this answer,

1. The base fee per gas (lets call it X) is the fee per unit gas. This value is not going to change (unless its modified in the protocol).
2. The amount of gas (lets call it Y) required per transaction will vary depending on the transaction.

total fee = amount of gas * fee per unit gas = Y * X

Which is why I recommended to use estimateGas() function.