https://medium.com/javascript-in-plain-english/how-memory-management-works-in-javascript-43e1ef22c3bb?source=friends_link&sk=1ba8029f600b1ef66388b13107440a9c

memory-management-explained.js

const events = require("events");

// Vars
let interestedUsers = [];
const goodPlanTopic = new events.EventEmitter();

function startListeningForMessages(topic, listeningUsers) {
  // Each time a message is received, we sent a notification to user interest in our topic
  function onNewMessage(newMessage) {
    listeningUsers.forEach(user =>
      console.log("Sent message to [" + user + "] : " + newMessage),
    );
  }

  // Subscribe to topic
  topic.on("message", onNewMessage);

  // We return function used to cancel listener
  return () => topic.off("message", onNewMessage);
}

// Every second we have a new appearing message (pushed in emitter).
setInterval(() => {
  goodPlanTopic.emit(
    "message",
    "Text message N°" +
      Math.random()
        .toFixed(6)
        .substr(2),
  );
}, 1000);

// Start programm
startListeningForMessages(goodPlanTopic, interestedUsers); // We are passing our array

console.log("Started, wait 10 seconds before first event…");

// Every ten seconds, we add or remove a new random user to the interested users list

// First scenario by re-assigning value

// setInterval(() => {
//   if (Math.random > 0.5) {
//     console.log("New user will be removed (but not repercuted)");
//     interestedUsers = interestedUsers.splice(
//       Math.floor(Math.random() * interestedUsers.length),
//       1,
//     );
//   } else {
//     console.log("New user will be added (but not repercuted)");
//     interestedUsers = [].concat(interestedUsers).push(
//       "user" +
//         Math.random()
//           .toFixed(3)
//           .substr(2),
//     );
//   }
// }, 10000);

// Second scenario by mutating
setInterval(() => {
  if (Math.random > 0.5) {
    console.log("New user will be removed (and repercuted)");
    interestedUsers.splice(
      Math.floor(Math.random() * interestedUsers.length),
      1,
    );
  } else {
    console.log("New user will be added (and repercuted)");
    interestedUsers.push(
      "user" +
        Math.random()
          .toFixed(3)
          .substr(2),
    );
  }
}, 10000);