cache.js

import { differenceInMilliseconds, differenceInSeconds } from "date-fns";

export class Cache {
	constructor({ minInterval = 1000 }) {
		this.minInterval = minInterval;
		this._map = new Map();
	}

	// Key could be an item here
	check = (key) => {
		const existing = this._map.get(key);
		if(existing !== undefined) {
			// Value was found, check if it's longer than a second ago.
			// calculate a difference in seconds
			const diff = differenceInMilliseconds(new Date(), existing);
			if(diff >= this.minInterval) {
				// All good, you can modify the value.
				this._map.set(key, new Date());
				return true;

			} else {
				// Smaller than one second, return false and don't update the item.
				return false;
			}
		}
		else { 
			// Doesn't exist yet
			this._map.set(key, new Date())
			return true;
		}
	}	
}

index.js

import { EventEmitter } from "events";
import { Cache } from "./cache.js";
const cache = new Cache({ minInterval: 1000 });

const emitter = new EventEmitter();

let transactions = [];

const eventListener = emitter.addListener('addTransaction', (data) => {
	// Check if we can add
	const permitted = cache.check(data.id);
	if (permitted) {
		transactions.push(data);
		console.log('Received a new transaction ', data);
	} else {
		console.log('Transaction recently modified, please wait a second.')
	}
})

const eventListener2 = emitter.addListener('removeTransaction', (data) => {
	const permitted = cache.check(data.id);
	if (permitted) {
		transactions = transactions.filter((e) => e.id !== data.id);
		console.log('Received a new transaction ', data);
	} else {
		console.log('Transaction recently modified, please wait a second.')
	}
})

function sleep(ms) {
	return new Promise(resolve => setTimeout(resolve, ms));
}

const run = async () => {
	for (let i = 0; i < 500; i++) {
		emitter.emit('addTransaction', { "data": "New stock added", id: "perkele" })
		await sleep(500);
	}
}

run();