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/**
* @license
* Copyright 2023 Google Inc.
* SPDX-License-Identifier: Apache-2.0
*/
import {describe, it, beforeEach} from 'node:test';
import expect from 'expect';
import sinon from 'sinon';
import {EventEmitter} from './EventEmitter.js';
describe('EventEmitter', () => {
let emitter: EventEmitter<Record<string, unknown>>;
beforeEach(() => {
emitter = new EventEmitter();
});
describe('on', () => {
const onTests = (methodName: 'on' | 'addListener'): void => {
it(`${methodName}: adds an event listener that is fired when the event is emitted`, () => {
const listener = sinon.spy();
emitter[methodName]('foo', listener);
emitter.emit('foo', undefined);
expect(listener.callCount).toEqual(1);
});
it(`${methodName} sends the event data to the handler`, () => {
const listener = sinon.spy();
const data = {};
emitter[methodName]('foo', listener);
emitter.emit('foo', data);
expect(listener.callCount).toEqual(1);
expect(listener.firstCall.args[0]).toBe(data);
});
it(`${methodName}: supports chaining`, () => {
const listener = sinon.spy();
const returnValue = emitter[methodName]('foo', listener);
expect(returnValue).toBe(emitter);
});
};
onTests('on');
// we support addListener for legacy reasons
onTests('addListener');
});
describe('off', () => {
const offTests = (methodName: 'off' | 'removeListener'): void => {
it(`${methodName}: removes the listener so it is no longer called`, () => {
const listener = sinon.spy();
emitter.on('foo', listener);
emitter.emit('foo', undefined);
expect(listener.callCount).toEqual(1);
emitter.off('foo', listener);
emitter.emit('foo', undefined);
expect(listener.callCount).toEqual(1);
});
it(`${methodName}: supports chaining`, () => {
const listener = sinon.spy();
emitter.on('foo', listener);
const returnValue = emitter.off('foo', listener);
expect(returnValue).toBe(emitter);
});
};
offTests('off');
// we support removeListener for legacy reasons
offTests('removeListener');
});
describe('once', () => {
it('only calls the listener once and then removes it', () => {
const listener = sinon.spy();
emitter.once('foo', listener);
emitter.emit('foo', undefined);
expect(listener.callCount).toEqual(1);
emitter.emit('foo', undefined);
expect(listener.callCount).toEqual(1);
});
it('supports chaining', () => {
const listener = sinon.spy();
const returnValue = emitter.once('foo', listener);
expect(returnValue).toBe(emitter);
});
});
describe('emit', () => {
it('calls all the listeners for an event', () => {
const listener1 = sinon.spy();
const listener2 = sinon.spy();
const listener3 = sinon.spy();
emitter.on('foo', listener1).on('foo', listener2).on('bar', listener3);
emitter.emit('foo', undefined);
expect(listener1.callCount).toEqual(1);
expect(listener2.callCount).toEqual(1);
expect(listener3.callCount).toEqual(0);
});
it('passes data through to the listener', () => {
const listener = sinon.spy();
emitter.on('foo', listener);
const data = {};
emitter.emit('foo', data);
expect(listener.callCount).toEqual(1);
expect(listener.firstCall.args[0]).toBe(data);
});
it('returns true if the event has listeners', () => {
const listener = sinon.spy();
emitter.on('foo', listener);
expect(emitter.emit('foo', undefined)).toBe(true);
});
it('returns false if the event has listeners', () => {
const listener = sinon.spy();
emitter.on('foo', listener);
expect(emitter.emit('notFoo', undefined)).toBe(false);
});
});
describe('listenerCount', () => {
it('returns the number of listeners for the given event', () => {
emitter.on('foo', () => {});
emitter.on('foo', () => {});
emitter.on('bar', () => {});
expect(emitter.listenerCount('foo')).toEqual(2);
expect(emitter.listenerCount('bar')).toEqual(1);
expect(emitter.listenerCount('noListeners')).toEqual(0);
});
});
describe('removeAllListeners', () => {
it('removes every listener from all events by default', () => {
emitter.on('foo', () => {}).on('bar', () => {});
emitter.removeAllListeners();
expect(emitter.emit('foo', undefined)).toBe(false);
expect(emitter.emit('bar', undefined)).toBe(false);
});
it('returns the emitter for chaining', () => {
expect(emitter.removeAllListeners()).toBe(emitter);
});
it('can filter to remove only listeners for a given event name', () => {
emitter
.on('foo', () => {})
.on('bar', () => {})
.on('bar', () => {});
emitter.removeAllListeners('bar');
expect(emitter.emit('foo', undefined)).toBe(true);
expect(emitter.emit('bar', undefined)).toBe(false);
});
});
describe('dispose', () => {
it('should dispose higher order emitters properly', () => {
let values = '';
emitter.on('foo', () => {
values += '1';
});
const higherOrderEmitter = new EventEmitter(emitter);
higherOrderEmitter.on('foo', () => {
values += '2';
});
higherOrderEmitter.emit('foo', undefined);
expect(values).toMatch('12');
higherOrderEmitter.off('foo');
higherOrderEmitter.emit('foo', undefined);
expect(values).toMatch('121');
});
});
});
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