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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...
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Tobias Nickel •

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 😊

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Sean Welsh Brown •

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!

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pentacular •

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

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Kaique 3.0 •

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);
   }
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Just do:

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

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

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Miguel Manjarres •

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

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Sofia Levin •

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

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Sean Welsh Brown •

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.

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Lalit Kumar •

Thanks for posting this, but it would be great if you can also add the time complexity of get and put methods.

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Ghanshyam •

Thank you for posting this. This is really helpful. I liked explanations and clean code.

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Vedansh bisht •

great post man, very helpful. Since recently heard about this ds, would try to implement in my project.

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paras231 •

great post thanks