Most Visited Sequence

index.js

const SEPARATOR = ':::';

module.exports = (function() {
    const cls = function() {
        this.userVisits = {};
    };

    const parseSequences = function(userVisits, length) {
        const sequences = {};
        const size = length - 1;

        for (let i = 0; i < userVisits.length; i++) {
            const visits = userVisits[i];
            const limit = visits.length - size;

            for (let j = 0; j < limit; j++) {
                const key = visits.slice(j, j + size).join(SEPARATOR);

                if (typeof sequences[key] === 'undefined')
                    sequences[key] = 0;
                
                sequences[key]++;
            }
        }

        return sequences;
    }

    cls.prototype.visit = function(user, page) {
        const key = 'user' + user;

        this.userVisits[key] ||= [];
        this.userVisits[key].push(page);
    };

    cls.prototype.getMostVisitedSequence = function(length) {
        const sequences = parseSequences(this.userVisits, length);
        const largest = {key: '', value: 0};

        for(let key in sequences) {
            if (sequences[key] <= largest.value)
                continue;
            
            largest.key = key;
            largest.value = sequences[key];
        }

        return largest.key.split(SEPARATOR);
    };

    return cls;
})();

test.js

const Subject = require('./index.js');

function testSequence1() {
    const subject = new Subject();
    // adicionar visitas
    subject.visit(1, 'A');
    subject.visit(2, 'B');
    subject.visit(1, 'C');
    subject.visit(2, 'A');
    subject.visit(2, 'C');
    subject.visit(1, 'D');
    subject.visit(2, 'D');

    // testar resultado
    console.log(assertSequence(subject.getMostVisitedSequence(3), ['A', 'C', 'D']) ? '.' : 'F');
}

function assertSequence(sequence, assertion) {
    if (sequence.length !== assertion.length)
        return false;

    for (let i = 0; i < sequence.length; i++) {
        if (sequence[i] !== assertion[i])
            return false;
    }

    return true;
}

testSequence1();

The for loop in line :12 wouldn't work because userVisits is an object. I'd have to either iterate through its value by using Object.values(userVisits) or by using the for..in construct.