Create an LRU in javascript

lru.js

const NEWER = Symbol("newer");
const OLDER = Symbol("older");

class LRU {
  constructor(limit = 10) {
    this.limit;
    this.size;
    this.cache = new Map();
    this.newest = undefined;
    this.oldest = undefined;
  }

  get(key) {
    const entry = this.cache.get(key);
    if (!entry) {
      console.log("No entry found");
      return;
    }
    this.markAsUsed(entry);
    return entry.value;
  }

  set(key, value) {
    let entry = this.cache.get(key);

    if (entry) {
      entry.value = value;
      this.markAsUsed(entry);
      return this;
    }

    // no entry;
    const newNode = new createNode(key, value);
    entry = this.cache.set(newNode);

    if (this.newest) {
      this.newest[NEWER] = entry;
      entry[OLDER] = this.newest;
    } else {
      this.oldest = entry;
    }

    this.newest = entry;
    ++this.size;
    if (this.size > this.limit) {
      // we hit the limit remove the head
      this.shift();
    }
  }

  shift() {
    // if (that's the only node remove);
    const entry = this.oldest;

    if (entry) {
      if (this.oldest[NEWER]) {
        this.oldest = this.oldest[NEWER];
        this.oldest[OLDER] = undefined;
      } else {
        this.oldest = undefined;
        this.newest = undefined;
      }

      entry[NEWER] = entry[OLDER] = undefined;
      this.cache.delete(entry.key);
      --this.size;
      return [entry.key, entry.value];
    }

    // remove the head;
  }

  markAsUsed(entry) {
    if (this.newest === entry) {
      return;
    }

    if (entry[NEWER]) {
      // A B C D E
      // if entry = A
      // it sets B(entry[newer]) as the oldest
      if (this.oldest === entry) {
        this.oldest = entry[NEWER];
      }
      // point C <- E
      entry[NEWER][OLDER] = entry[OLDER];
    }

    if (entry[OLDER]) {
      entry[OLDER][NEWER] = entry[NEWER];
    }

    // change entry new and old
    entry[NEWER] = undefined;
    entry[OLDER] = this.newest;

    // change the newest
    if (this.newest) {
      this.newest[NEWER] = entry;
    }
    this.newest = entry;
  }

  toString() {
    let s;
    entry = this.oldest;

    while (entry) {
      s += `${this.entry.key} : ${this.entry.value}`;
      entry = entry[NEWER];
      if (entry) {
        s += " < ";
      }
    }
    return s;
  }
}