Contract Event Logging

Introduction

Contract events is a way for contracts to deliver event-like information to third-party (off-chain) applications. It can be emitted by using the EMIT instruction in Michelson.

For more details and examples of how the EMIT instruction works, refer to this article.

Subscribing to Events in Taquito

Taquito provides a simple way for users to subscribe to certain events on the blockchain via the PollingSubscribeProvider.

Example

Usage

const Tezos = new TezosToolkit(RPC_URL);

Tezos.setStreamProvider(
  Tezos.getFactory(PollingSubscribeProvider)({
    shouldObservableSubscriptionRetry: true, 
    pollingIntervalMilliseconds: 1500 
  })
);

try {
  const sub = Tezos.stream.subscribeEvent({
    tag: 'tagName',
    address: 'KT1_CONTRACT_ADDRESS'
  });
    
  sub.on('data', console.log);
    
} catch (e) {
  console.log(e);
}

• tag is the tag string that was defined in the smart contract with the EMIT instruction
• address is the address of the smart contract that was called

info

If you would like to subscribe to any event that goes through, you can call subscribeEvent() as is without any parameters

Output

The output of the subscribeEvent method will look something like this:

{
  "opHash": "oopRTC5iNxssoC5dAz54u7uthUz6xBayaSPcLXhkLwHGjuS7Bos",
  "blockHash": "BLCTEDjZDtuUcYxmSPXHn3XrKruub4NF4mzTgR2EbpPRFN7JzDV",
  "level": 313647,
  "kind": "event",
  "source": "KT1ACmSCoRsA69zHnv5mMBC4vdcxbFJpHRoo",
  "nonce": 0,
  "type": {
    "prim": "or",
    "args": [
      {
        "prim": "nat"
      },
      {
        "prim": "string"
      }
    ]
  },
  "tag": "first",
  "payload": {
    "prim": "Left",
    "args": [
      {
        "int": "10"
      }
    ]
  },
  "result": {
    "status": "applied",
    "consumed_milligas": "1000000"
  }
}