Caching is a common technique used to improve the performance of web applications by storing frequently accessed data in memory. However, one challenge in caching is when to evict or remove items from the cache to make space for new entries. In this blog post, we’ll explore how to implement a proxy-based cache eviction strategy in JavaScript.

The Proxy Object

JavaScript provides the Proxy object, which allows us to intercept and customize operations performed on an object. We can leverage this functionality to implement our cache eviction strategy.

Cache Implementation

First, let’s create a basic cache implementation using a JavaScript object:

const cache = {};

function getValue(key) {
  return cache[key];
}

function setValue(key, value) {
  cache[key] = value;
}

Tracking Last-Accessed Time

To implement our cache eviction strategy, we need to keep track of the last time each cache item was accessed. We can achieve this by storing the timestamp alongside the value in the cache object.

const cache = {};

function getValue(key) {
  const item = cache[key];
  if (item) {
    item.lastAccessed = Date.now();
    return item.value;
  }
  return undefined;
}

function setValue(key, value) {
  cache[key] = {
    value,
    lastAccessed: Date.now(),
  };
}

Evicting Items from the Cache

Now, we can implement the eviction logic. We’ll create a function that checks if the cache is full and, if so, removes the least recently accessed item.

const cache = {};
const maxCacheSize = 10;

function getValue(key) {
  // ...
}

function setValue(key, value) {
  // ...
  evictIfNeeded();
}

function evictIfNeeded() {
  if (Object.keys(cache).length >= maxCacheSize) {
    const leastRecentlyAccessed = Object.keys(cache).reduce((a, b) =>
      cache[a].lastAccessed < cache[b].lastAccessed ? a : b
    );
    delete cache[leastRecentlyAccessed];
  }
}

Implementing the Proxy

To incorporate the eviction logic seamlessly into our cache, we can use the Proxy object. We’ll create a proxy around our cache object and override the get and set trap methods to include the eviction logic.

const cache = new Proxy({}, {
  get(target, key) {
    const value = target[key];
    if (value) {
      value.lastAccessed = Date.now();
      return value.value;
    }
    return undefined;
  },
  set(target, key, value) {
    target[key] = {
      value,
      lastAccessed: Date.now(),
    };
    evictIfNeeded();
    return true;
  },
});

Conclusion

In this blog post, we explored how to implement a proxy-based cache eviction strategy in JavaScript. By incorporating the Proxy object and tracking the last-accessed time of cache items, we can automatically evict least recently used entries to make space for new ones. This approach can greatly improve the performance of our applications by efficiently managing memory usage.

#programming #javascript