docs: function CacheEntry(value, createdAt, lastAccessedAt){
    this.value = value;
    this.createdAt = createdAt || Date.now();
    this.lastAccessedAt = lastAccessedAt || this.createdAt;
  
    if (typeof this.createdAt !== 'number' ||
      typeof this.lastAccessedAt !== 'number'){
      throw new Error('Expecting date in timestamp format or use CacheEntry.parse method instead');
    }
  }