JavaScript Engineering

Interaction patterns, state handling, and data-driven UI logic without overcomplicating the stack.

Stateful dashboard interactions

const dashboardState = {
    mode: "monthly",
    data: {
        monthly: { reports: 2847, timeSaved: 1240 },
        quarterly: { reports: 8310, timeSaved: 3720 }
    }
};

function setDashboardMode(mode) {
    if (!dashboardState.data[mode]) return;
    dashboardState.mode = mode;
    renderDashboard();
}

function renderDashboard() {
    const { reports, timeSaved } = dashboardState.data[dashboardState.mode];
    document.querySelector("[data-kpi='reports']").textContent =
        reports.toLocaleString();
    document.querySelector("[data-kpi='time-saved']").textContent =
        timeSaved.toLocaleString();
}

document.querySelectorAll("[data-mode-toggle]").forEach(button => {
    button.addEventListener("click", () => {
        setDashboardMode(button.dataset.modeToggle);
    });
});

renderDashboard();

Accessible modal controller

function createModalController(root) {
    const openButtons = document.querySelectorAll("[data-open-modal]");
    const closeButtons = root.querySelectorAll("[data-close-modal]");
    const dialog = root.querySelector("[role='dialog']");

    function openModal() {
        root.hidden = false;
        dialog.focus();
        document.body.style.overflow = "hidden";
    }

    function closeModal() {
        root.hidden = true;
        document.body.style.overflow = "";
    }

    openButtons.forEach(btn => btn.addEventListener("click", openModal));
    closeButtons.forEach(btn => btn.addEventListener("click", closeModal));

    root.addEventListener("click", event => {
        if (event.target === root) closeModal();
    });

    document.addEventListener("keydown", event => {
        if (event.key === "Escape" && !root.hidden) closeModal();
    });
}

Patterns for real systems

Practical vanilla JS patterns used in fraud, collections, and QA tooling.

Debounced search

function debounce(fn, delay = 250) {
    let handle;
    return function (...args) {
        clearTimeout(handle);
        handle = setTimeout(() => fn.apply(this, args), delay);
    };
}

const searchInput = document.querySelector("[data-search]");

searchInput.addEventListener(
    "input",
    debounce(event => {
        const value = event.target.value.trim();
        fetch("/api/accounts?query=" + encodeURIComponent(value));
    }, 300)
);

Client-side feature flags

const flags = new Map([["newCollectionsView", true]]);

export function isFeatureEnabled(name) {
    return flags.get(name) === true;
}

Form validation

const form = document.querySelector("[data-form='qa-score']");

form.addEventListener("submit", event => {
    const score = Number(form.elements["score"].value);
    if (Number.isNaN(score) || score < 0 || score > 100) {
        event.preventDefault();
        alert("Score must be between 0 and 100.");
    }
});