chain_getBlockHash - Asset Hub RPC Method

Returns the block hash for a given block number on Asset Hub. This is the primary method for converting block numbers into block hashes, which are required by most other chain RPC methods.

Why Asset Hub? Build on Polkadot's system parachain managing $4.5B+ in DOT tokens, native USDC/USDT, and NFTs with 50-90% lower fees than Relay Chain, fee payment in any supported asset, 1.5M+ accounts migrated, and trustless Ethereum bridge access.

When to Use This Method

chain_getBlockHash is fundamental for asset issuers, stablecoin integrators, and teams requiring low-cost token management on Polkadot:

• Historical Queries — Convert block numbers to hashes for state queries at specific heights on Asset Hub
• Block Navigation — Navigate the blockchain history for native stablecoin transfers (USDC, USDT), DOT staking and governance, and cross-chain asset management via XCM
• Data Indexing — Build block number-to-hash mappings for indexers and explorers
• Cross-Reference — Translate block numbers from events or logs into hashes for detailed lookups

Code Examples

Common Use Cases

1. Block Range Iterator

Iterate over a range of blocks on Asset Hub for indexing:

async function iterateBlocks(api, startBlock, endBlock) {
  for (let num = startBlock; num <= endBlock; num++) {
    const hash = await api.rpc.chain.getBlockHash(num);
    const block = await api.rpc.chain.getBlock(hash);

    console.log(`Block #${num}: ${block.block.extrinsics.length} extrinsics`);
  }
}

2. Historical State Query

Query Asset Hub state at a specific block height:

async function getBalanceAtBlock(api, address, blockNumber) {
  const blockHash = await api.rpc.chain.getBlockHash(blockNumber);
  const apiAt = await api.at(blockHash);
  const account = await apiAt.query.system.account(address);

  return {
    blockNumber,
    free: account.data.free.toString(),
    reserved: account.data.reserved.toString()
  };
}

3. Genesis Hash Verification

Verify you are connected to the correct Asset Hub network:

async function verifyNetwork(api, expectedGenesisHash) {
  const genesisHash = await api.rpc.chain.getBlockHash(0);

  if (genesisHash.toHex() !== expectedGenesisHash) {
    throw new Error(`Wrong network! Expected ${expectedGenesisHash}, got ${genesisHash.toHex()}`);
  }

  console.log('Connected to correct network');
}

Error Handling

Related Methods

• chain_getBlock — Get full block data by hash
• chain_getHeader — Get block header by hash
• chain_getFinalizedHead — Get the latest finalized block hash