2020 - JS interview - later solutions (mine)

// 1)
function findServer(servers, check) {
    const len = servers.length;
    if (len === 0) {
        return Promise.resolve(null);
    }

    const srvIndex = len / 2;
    const current = servers[srvIndex];

    return check(current).then(checkRes => {
        if (len === 1 && !checkRes) {
            return Promise.resolve(current);
        }

        if (checkRes) {
            // Current server is Ok
            // Look to the right
            return findServer(servers.slice(srvIndex, len), check);
        } else {
            // Current server is not Ok
            // Result is current or to the left of current
            // Must confirm that current is first or find one from the left
            return findServer(servers.slice(0, srvIndex), check).then(leftFindServerResult => {
                if (leftFindServerResult) {
                    // findServer() from left is not null => found result earlier in the array
                    return Promise.resolve(leftFindServerResult);
                } else {
                    // Nothing found to the left of current, returning current
                    return Promise.resolve(current);
                }
            })
        }
    });
}


// 2)
const queue = new Map();
const orderedPrioList = [];

let runningPrio = null;
let runningUrls = new Set();

function addToQueue(cb, prio) {
    const existing = queue.get(prio);
    let arr = [];
    if (existing) {
        arr = existing.value;
    }
    arr.push(cb);
    queue.set(prio, arr);
}

function addPrio(prio) {
    if (orderedPrioList.findIndex(prio) !== -1) {
        return;
    }
    orderedPrioList.push(prio);
    orderedPrioList.sort((a, b) => a - b);
}

function startNewPrio() {
    if (orderedPrioList.length === 0) {
        return;
    }

    if (runningPrio !== null) {
        queue.delete(runningPrio);
        runningPrio = null;
    }

    const runningPrio = orderedPrioList.pop();
    const qbList = queue.get(runningPrio);

    for(const cb of qbList) {
        cb();
    }
}

function load(url, priority) {
    return new Promise((res, reject) => {
        const jobCb = () => {
            runningUrls.add(url);
            try {
                const data = await loadData(url);
                res(data);
            } catch (msg) {
                reject(msg);
            }
            runningUrls.delete(url);

            if (runningUrls.size === 0) {
                startNewPrio();
            }
        };

        // runningPrio === null means queue is empty
        if (!runningPrio || runningPrio === priority) {
            runningPrio = priority;
            runningUrls.add(url);
            jobCb();
        } else {
            addPrio(priority);
            addToQueue(jobCb, priority);
        }
    });
}


// 3)
function camelToSnake(str) {
    return str.replace(/[A-Z]/g, (m) => `_${m.toLowerCase()}`);
}