events.md

Chapter 13: Events

Our contract is almost finished! Now let's add an event.

Events are a way for your contract to communicate that something happened on the blockchain to your app front-end, which can be 'listening' for certain events and take action when they happen.

Example

# declare an event
event NewPersonAdded:
    name: String[64]
    age: uint256

people: HashMap[String[64], uint256]

@external
def addNewPerson(name: String[64], age: uint256):
    self.people[name] = age

    # fire an event to let the app know the function was called
    log NewPersonAdded(name, age)

Your app front-end could then listen for the event. A javascript implementation would look something like:

YourContract.NewPersonAdded(function(error, result) {
  // do something with result
}

Put it to the test

We want an event to let our front-end know every time a new pokemon was created, so the app can display it.

1. Create an event named NewPokemonCreated. It should have 3 arguments:

• name of String[32] type
• dna of uint256 type
• HP of uint256 type

2. Use the log keyword to fire the event inside the _createPokemon function just before the return statement.

** Template **

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** Solution **

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** Previous Chapter Solution **

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