You can find all the code in this post at repo Github.
Design Pattern related challenges
Event Emitter
class EventEmitter {
constructor() {
this._events = Object.create(null);
this._key = 0;
}
on(eventName, listener) {
if (!Object.hasOwn(this._events, eventName)) {
this._events[eventName] = {};
}
const listenerId = this._key;
this._key += 1;
this._events[eventName][listenerId] = listener;
return {
off: () => {
delete this._events[eventName][listenerId];
}
}
}
emit(eventName, ...args) {
if (
!Object.hasOwn(this._events, eventName) ||
!Object.keys(this._events[eventName]).length
) {
return false;
}
const listeners = { ...this._events[eventName] };
Object.values(listeners).map((listener) => {
listener.call(null, ...args);
});
return true;
}
once(eventName, listener) {
const subscription = this.on(eventName, (...args) => {
subscription.off();
listener(...args);
});
return subscription;
}
}
// Usage example
const emitter = new EventEmitter();
function addTwoNumbers(a, b) {
console.log(`The sum is ${a + b}`);
}
const sub = emitter.on('foo', addTwoNumbers);
emitter.emit('foo', 1, 2);
// => "The sum is 3"
emitter.on('foo', (a, b) => {
console.log(`The product is ${a * b}`);
});
emitter.emit('foo', 4, 5);
// > "The sum is 9"
// > "The product is 20"
sub.off();
emitter.emit('foo', -3, 9);
// > "The product is -27"
// (Only the multiply callback is triggered, the first one was unsubscribed.)
emitter.once('bar', (x) => {
console.log(`Bar was called with ${x}`);
});
emitter.emit('bar', 1); // Logs: "Bar was called with 1"
emitter.emit('bar', 2); // Does nothing, the listener was already removed
Singleton
const globalMap = new Map();
export default {
getInstance() {
return globalMap;
},
};
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