Linked list exercise

least frequently used cache.js

class LFUCache {
    constructor(capacity) {
        this.capacity = capacity;
        this.lru = [];
        this.cache = Object.create(null, {});
    }

    get(key) {
        if (!this.cache[key]) return -1;
        
        this.cache[key].usage += 1;
        
        return this.cache[key].value;
    }

    set(key, val) {
        let addNewCacheItem = false;
        
        this.cache[key] = {
            ...this.cache[key],
            usage: this.cache?.[key]?.usage ?? 0,
            value: val,
            lruKey: key,
        };
        
        const isExistingIndex = this.lru.findIndex(({ lruKey}) => lruKey === key);
        if (isExistingIndex > -1) {
            this.lru[isExistingIndex] = this.cache[key];
        } else {
            addNewCacheItem = true;
        }
        
        if (this.lru.length > this.capacity) {
            const { lruKey } = this.lru.sort((x, y) => {
                if (x.usage >= y.usage) return 1;
                else return -1;
            })
            .shift();
            
            delete this.cache[lruKey];
            
            if (addNewCacheItem) {
                this.lru.push(this.cache[key]);
            }
        }
    }
}