eth_chainId

Read the EVM network Chain ID currently selected by the wallet. DApps can use this to determine whether the user is on the target network and avoid sending signatures or transactions to the wrong chain.

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Inputs

none

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return value

string - ​​Chain ID, returned as a hex string beginning with 0x.

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Demo

const chainId = await window.$ukey.ethereum.request({
  method: "eth_chainId",
});

console.log("Chain ID in hex:", chainId);
console.log("Chain ID in decimal:", parseInt(chainId, 16));

Identify the current network

const CHAIN_IDS = {
  ETHEREUM: "0x1",
  POLYGON: "0x89",
  BSC: "0x38",
  ARBITRUM: "0xa4b1",
  OPTIMISM: "0xa",
  BASE: "0x2105",
};

async function readCurrentChain() {
  const chainId = await window.$ukey.ethereum.request({
    method: "eth_chainId",
  });

  switch (chainId) {
    case CHAIN_IDS.ETHEREUM:
      console.log("Now connected to Ethereum Mainnet");
      break;
    case CHAIN_IDS.POLYGON:
      console.log("Now connected to Polygon");
      break;
    default:
      console.log("Chain connection established:", parseInt(chainId, 16));
  }

  return chainId;
}

Ask the user to switch to a specified network

async function ensureChainSelected(requiredChainId) {
  const chainId = await window.$ukey.ethereum.request({
    method: "eth_chainId",
  });

  if (chainId !== requiredChainId) {
    try {
      await window.$ukey.ethereum.request({
        method: "wallet_switchEthereumChain",
        requestParams: [{ chainId: requiredChainId }],
      });
    } catch (error) {
      if (error.code === 4902) {
        throw new Error("Add this network to the wallet first");
      }
      throw error;
    }
  }
}

// Note: use
await ensureChainSelected("0x1"); // Note: Requires Ethereum mainnet

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Common chain ID

Network	Hex	Decimal
Ethereum mainnet	0x1	1
Goerli Testnet	0x5	5
Sepolia Testnet	0xaa36a7	11155111
Polygon	0x89	137
BSC	0x38	56
Arbitrum One	0xa4b1	42161
Optimism	0xa	10
Base	0x2105	8453
Avalanche C-Chain	0xa86a	43114

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error code

Code	Message	Details
-32603	Provider internal failure	Provider returned an internal failure

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illustrate

• The return value is always a hex string beginning with 0x.
• Monitoring chainChanged can detect when the user switches networks on the wallet side.
• After receiving a network switching event, re-read the chain-related configuration, contract address and balance information.
• Follows EIP-695 specification.

window.$ukey.ethereum.on("chainChanged", (chainId) => {
  console.log("Network has switched to:", chainId);
  // Suggested action: reload the page
  window.location.reload();
});