Context

The context of an event listener refers to the value of this when a listener function is invoked. This allows you to control what this points to inside your event handler, which can be useful for maintaining state or accessing properties from a specific object.

How context works

When you add a listener (using on, once, or addListener), you can provide an optional context argument as the third parameter, usually an object.

When the event is emitted, the listener function is called with this set to the provided context. If no context is provided, the ESMitter instance itself is used as the default context.

Example

class MyClass extends ESMitter<{
  success: ESMitterEvent<[{ foo: string; bar: string }]>;
  error: ESMitterEvent<[number, string]>;
}> {}

const instance = new MyClass();

const context = { value: 42 };

function handler() {
  console.log(this.value); // Will log 42
}

instance.on("success", handler, context);
instance.emit("success"); // Logs: 42

API Reference

• addListener(event, fn, context?, once?)
• on(event, fn, context?)
• once(event, fn, context?)
• removeListener(event, fn?, context?, once?)

All these methods accept a context parameter to control the value of this inside the listener function.