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    0.0.7 • Public • Published

    Event Well Crank

    @completium/event-well-crank detects events emitted by smart contracts on the Tezos blockchain, and executes registered event handler functions.



    Registers an event handler for a specific contract. It takes 3 arguments:

    • the address of the emitter contract
    • the function to create an event from its packed version
    • the event handler function that takes 2 arguments:
      • the emitted event
      • the event data (optional)

    The function to create the event may be automatically generated (see Bindings below).

    The event data provides information about the emitted event:

    • date
    • block hash
    • operation hash
    • source of the event (account address at the source of the event emission)


    Starts the crank process. It takes an optional CrankOptions object with optional fields:

    Field Type Default Desc
    bottom string head~4 block hash to start crawling from
    delay number 2000 number of milliseconds between two lookups of the event well contract
    horizon number 3 number of blocks to look back (the higher, the higher the probability to read the main branch)
    endpoint string endpoint used by the event crank
    well string (see below) address of the event well contract
    verbose boolean false flag to turn crank's verbose mode on/off

    The well contract is deployed on mainnet and testnets:

    Network Well address
    mainnet KT1AHVF5m8XaWPQCGgfAsZ9eSJJZ7WVGV2hE
    ithacanet KT1ReVgfaUqHzWWiNRfPXQxf7TaBLVbxrztw
    hangzhounet KT1Aho6K97CKApDSCxXEzvP14qd1qTHhF4uH


    Stops the crank.


    @completium/completium-cli generates the TS bindings from an Archetype contract. It generates for each event emitted by a contract:

    • the event type
    • the make event function
    • the dedicated register function (calls register function with generated make function), which takes 2 arguments:
      • the address of the emitter contract
      • the event handler function

    The completium CLI command to generate the bindings:

    $ completium-cli generate bindings-ts mycontract.arl > mycontract-bindings.ts


    This example illustrates how to emit event from a smart contract and how to receive them in a Dapp.

    Emit event

    Declare the event type with the event declaration and emit an event with the emit instruction:

    archetype event_demo
    event TestEvent {
      val: string
    entry emit_event(v : string) {
      if length(v) > 20 then
        emit<TestEvent>({ val })

    Deploy the contract on the testnet with the following command:

    $ completium-cli set endpoint
    $ completium-cli deploy event_demo.arl

    Receive event

    Generate bindings with the following command:

    $ completium-cli generate bindings-ts event_demo > bindings-event_demo.ts

    It generates the following two elements:

    • EventDemo
    • register_TestEvent

    These elements may be used to implement the event receiver application which registers an event handler and starts the cranks. Say the event demo contract deployed above is at address KT19EAMugKU416cbA9jL1XcukWArfpv4dLYA

    import { runCrank } from '@completium/event-well-crank';
    import { register_TestEvent, TestEvent } from './bindings-event_demo';
    const handleTestEvent = (e : TestEvent) => {
      console.log(`Test Event received with value "${e.val}"!`);
    const run = async () => {
      register_TestEvent('KT19EAMugKU416cbA9jL1XcukWArfpv4dLYA', handleTestEvent);
        endpoint: '',
        well: 'KT1ReVgfaUqHzWWiNRfPXQxf7TaBLVbxrztw'
    await run()


    Compile and run the application above. Then call the contract with the following command:

    $ completium-cli call event_demo --arg `{ "v" : "This is a long enough string." }`

    After a few blocks generation, the application prints the following message:

    Test Event received with value "This is a long enough string."!


    npm i @completium/event-well-crank

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