<pre class="shiki github-dark shaku"><code>class EventEmitter { subscriptions = new Map(); subscribe(eventName, callback) { if(!this.subscriptions.has(eventName)){ this.subscriptions.set(eventName, new Set()); // Set optimizes delete in O(1) compared to O(n) in array } 	const subscription = this.subscriptions.get(eventName); // Create new ref for each subscription even for same callback. // Else 2 issues: 1.deleting this will delete the cb 2. If same cb called will get overridden in set let callbackObj = {callback}; subscription.add(callbackObj); return { // Use arrow function to have lexical binding of this.subscriptions. // Else sub1.release will make this.subscriptions undefined release: () =&gt; { subscription.delete(callbackObj); if(subscription.size === 0){ this.subscriptions.delete(eventName); // Use the delete mehod of native Map Instance } } } } emit(eventName, ...args) { 	if(!this.subscriptions.has(eventName)) return; const subscription = this.subscriptions.get(eventName); for(let callbackObj of subscription){ callbackObj.callback.apply(this, args); } }}</code></pre>

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There is Event Emitter in Node.js, Facebook once had its own implementation but now it is archived. You are asked to create an Event Emitter Class con…