Beefy justification subscription is not working

Question

I would like to subscribe to the beefy justification stream on Rococo. The rpc for getFinalizedHead works fine, but I also require the justifications themselves.

When I try to subscribe to the justifications using (in the polkadot-apps-ui/Developer/Javascript section):

const unsub = await api.rpc.beefy.subscribeJustifications((header) => {
     console.log(`The last block has a timestamp of ${header}`);
});

I get the following error (when a new header is finalized):

h@https://polkadot.js.org/apps/modu.151b50df8afdab63.js:50:76373
createTypeUnsafe@https://polkadot.js.org/apps/modu.151b50df8afdab63.js:50:163502
_formatOutput@https://polkadot.js.org/apps/modu.151b50df8afdab63.js:50:5692
_formatResult@https://polkadot.js.org/apps/modu.151b50df8afdab63.js:50:3182
d@https://polkadot.js.org/apps/modu.151b50df8afdab63.js:50:4503
21899/y/this.__internal__onSocketMessageSubscribe@https://polkadot.js.org/apps/modu.151b50df8afdab63.js:50:24109
21899/y/this.__internal__onSocketMessage@https://polkadot.js.org/apps/modu.151b50df8afdab63.js:50:23088

How can I get this to work?

Any help is much appreciated
Please and thank you

Answer 1

Thank you for reporting this !

Looks like the definition of beefy::subscribeJustifications() from polkadot-js/api is outdated. Published a PR that should fix it: https://github.com/polkadot-js/api/pull/5740 . The change will take effect after polkadot-js/apps is redeployed. Not sure exactly when this will happen, but will keep an eye on it.