[Javascript] Deep Search nested tag element in DOM tree

// For example you want to search for nested ul and ol in a DOM tree branch

// Give example <ol> <li> <ol> <li></li> </ol> </li> </ol> should retrun 2

function solution( tags = ['ul', 'ol']) {

　　const [uls, ols] = tags.map(tag => Array.from($(`${tag}`)));
　　const [logUl, logOl] = tags.map(tag => new Logger(`${tag}`));

　　deepSearch(uls, 'ul', logUl);
　　deepSearch(ols, 'ol', logOl);

　　return logUl.count + logOl.count;
}

class Logger {
    constructor(tag) {
        this.tag = tag;
        this.num = ;
    }

    get count () {
        return this.num;
    }

    get tagName () {
        return this.tag;
    }

    countOne() {
        this.num++;
    }
}

function deepSearch(els = [], tag = "", log) {

    // if no such elements passed in
    if (!els.length) {
        return;
    }

    log.countOne();

    // loop though the els and check whether contains tag
    els.forEach(el => {
        const targets = Array.from(el.getElementsByTagName(`${tag}`));
        if (targets.length) {
            deepSearch(targets, tag, log);
        }
    });
}