LRU cache

cache.js

const _ = require('lodash');
const LRU = require('lru-cache');

class Cache {
    constructor(maxSizeInMB = 128) {
        this.lru = new LRU({
            max: maxSizeInMB * 1e+6,
            length: n => Buffer.byteLength(n, 'utf8')
        });
    }

    max(MB) {
        this.lru.max = MB * 1e+6;
    }

    get(key) {
        return this.lru.get(key) || null;
    }

    set(key, value) {
        if (!_.isString(key) || !_.isString(value)) {
            throw new Error('key and value must be strings.');
        }
        
        return this.lru.set(key, value);
    }
}

module.exports = new Cache();

cache.spec.js

const chai = require('chai');

const cache = require('./cache');

const expect = chai.expect;

describe('libs/cache.js', () => {
    describe('max', () => {
        it('should change max', () => {
            expect(cache.lru.max).to.equal(128 * 1e+6);
            cache.max(0.000001);
            expect(cache.lru.max).to.equal(0.000001 * 1e+6);
        });
    });

    describe('get', () => {
        before(() => {
            cache.set('a', 'b');
        });

        it('should get', () => {
            expect(cache.get('a')).to.equal('b');
        });

        it('should get null', () => {
            expect(cache.get('b')).to.be.null;
        });
    });

    describe('set', () => {
        it('should not accept non stirng key', () => {
            expect(() => cache.set(1, 'a')).to.throw('key and value must be strings.');
        });

        it('should not accept non stirng key', () => {
            expect(() => cache.set('a', 1)).to.throw('key and value must be strings.');
        });

        it('should set and stale', () => {
            cache.set('b', 'c');
            expect(cache.get('a')).to.be.null;
            expect(cache.get('b')).to.equal('c');
            cache.set('c', 'd');
            expect(cache.get('b')).to.be.null;
            expect(cache.get('c')).to.equal('d');
        });
    });
});