DEV Community

Implementing a Simple LRU Cache in JavaScript

Sean Welsh Brown on September 03, 2020

In your travels as a software engineer, you're likely to come across instances where every possible data structure gets a chance to shine. One in p...

Read full post

Tobias Nickel • Sep 3 '20

when get a key and it is not there, I would return undefined or an error. -1 could also be the value. It reminds me to the time when we needed if (array.indexOf(needle)===-1)；{...} and today we have array.includes.

It is very interesting how you are using the iterator from cache.keys().

also, it would be interesting to add a time-to-life, but that can be a good homework 😊

Sean Welsh Brown • Sep 3 '20

Thanks for your feedback Tobias! I was wondering what the best return value would be for when a key wasn't found, you're definitely right about "undefined" or throwing an error being better than returning a string. I'll edit that part to make it a bit more clear.

Also a great suggestion to add a timed-life option, I'll start thinking about how to implement that!

pentacular • Sep 3 '20

Delegate the problem to the caller -- have them provide a value to return in the not-found case.

Kaique 3.0 • Oct 25 '24

a small improve to the code, instead of:

   if (this.cache.size === this.capacity) {
     this.cache.delete(this.cache.keys().next().value);
     this.cache.set(key, value);
   } else {
     this.cache.set(key, value);
   }

Just do:

   if (this.cache.size === this.capacity) {
     this.cache.delete(this.cache.keys().next().value);
   }
   this.cache.set(key, value);

Explorer • Dec 1 '24

For me, in general programming, readability is more important than writing short and fancy code.

Miguel Manjarres • Sep 4 '20

Is the first time I heard about this data structure, it seems very useful. Thanks for sharing! Awesome post and explanation

Sofia Levin • Sep 3 '20

Wow, TIL about Map objects. Great article, thanks for sharing!

Sean Welsh Brown • Sep 3 '20

You're very welcome! Thanks so much for reading. I only recently started learning about Map and Set objects myself, and about how they differ from standard JavaScript objects. They're super useful for certain situations like this.