SkeletonMFU.js

// We extend the map instead of composing it
// So that non-overridden functions are passed to the base
class MFUMap extends Map {

  // Private properties
  #frequencyMap = new Map();
  #maxSize = 10;

  constructor(size = 10) {
    super();
    this.#maxSize = size;
    debug(`Initialized map with size=${size}`);
  }

  // Check if our map size is going beyond maxSize
  #resizeMap = () => {
    // Drop entries from the map
  }

  #updateFrequency = key => {
    // Update frequency of the key here
  }

  // Override the get and set function of Map
  set(key, value) {
    let result =  super.set(key, value);

    // Update the frequency of the key
    this.#updateFrequency(key);

    return result;
  }

  get(key) {
    let exists = super.get(key);

    // Don't update non existing gets
    if (exists)
      this.#updateFrequency(key);

    return exists;
  }
}