Add blockHash parameter to Polkadot.js chainState query

Question

For a Polkadot parachain (Zeitgeist) query, I need to add the block hash to get historical data. See this example:

When I try to try to run the same query in polkadot.js, I get an error when I try and add a blockHash as a parameter

// This causes an error - how to provide block hash to this function?

const blockHash = "0x52352ca066543d41aacb0c6419e5bb7e2d9ee621b3d8dabe2c2174ce2c5f86c5"
const unixTimestamp = await api.query.timestamp.now(blockHash);

could you help me figure out how I should provide this parameter?

the error:

ba@https://polkadot.js.org/apps/modu.ac52cd44a2179bd7.js:1:79374
overrideNoSub@https://polkadot.js.org/apps/modu.ac52cd44a2179bd7.js:1:91709
10589/u/</<@https://polkadot.js.org/apps/modu.ac52cd44a2179bd7.js:1:105234
10589/u/</<@https://polkadot.js.org/apps/modu.ac52cd44a2179bd7.js:1:105195
10589/u/<@https://polkadot.js.org/apps/modu.ac52cd44a2179bd7.js:1:105338
anonymous/<@https://polkadot.js.org/apps/page.e64d864372c5d12b.js line 1464 > Function:4:49
anonymous@https://polkadot.js.org/apps/page.e64d864372c5d12b.js line 1464 > Function:7:67
30145/T</Z</<@https://polkadot.js.org/apps/page.e64d864372c5d12b.js:1464:1810

Answer 1

For querying anything historical in polkadot-js there is the .at property to the ApiPromise.

Example:

const block = '0x52352ca066543d41aacb0c6419e5bb7e2d9ee621b3d8dabe2c2174ce2c5f86c5'
const apiAt = await api.at(block);
const timestamp = await apiAt.query.timestamp.now();
console.log(timestamp);

I wrote a more in detail response on the .at for another user a while ago here: PolkadotJs Api: queryMulti with different blockHashes

Hope that helps :)

Answer 2

Found the following info (will try):

https://polkadot.js.org/docs/api/examples/promise/read-storage-at/