JavaScript Engineering

Building Interactive
Systems That Scale

Interaction patterns, state handling, and data-driven UI logic without overcomplicating the stack. Real patterns from fraud detection, collections management, and QA tooling at scale.

0
Production Apps
98%
Test Coverage
<200ms
Avg Response
0
Framework Lock-in

Live Code Playground

Edit the code and see results in real-time. Experiment with patterns used in production financial systems.

Console Output
// Click "Run Code" to execute

Core Interaction Patterns

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

📊

Stateful Dashboard

Interactive
Reports
2,847
Time Saved
1,240 hrs
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();
}
🔲

Accessible Modal

A11y Ready
function createModalController(root) {
    const dialog = root.querySelector("[role='dialog']");

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

    // Escape key closes modal
    document.addEventListener("keydown", (e) => {
        if (e.key === "Escape") closeModal();
    });
}
🔍

Debounced Search

Performance
  • PSL-22031 · Active
  • PSL-22044 · On hold
  • PSL-22098 · Escalated
function debounce(fn, delay = 250) {
    let handle;
    return function (...args) {
        clearTimeout(handle);
        handle = setTimeout(() => 
            fn.apply(this, args), delay);
    };
}

searchInput.addEventListener("input",
    debounce(e => {
        fetch(`/api/accounts?q=${e.target.value}`);
    }, 300)
);
🚩

Feature Flags

DevOps
newCollectionsViewON
agentAssistPanelOFF
darkModeToggleON
const flags = new Map([
    ["newCollectionsView", true],
    ["agentAssistPanel", false]
]);

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

// Usage in component
if (isFeatureEnabled("newCollectionsView")) {
    renderNewView();
}

Form Validation

UX
form.addEventListener("submit", event => {
    const score = Number(form.elements["score"].value);
    
    if (Number.isNaN(score) || score < 0 || score > 100) {
        event.preventDefault();
        showError("Score must be 0-100");
        return;
    }
    
    submitQAScore(score);
});
🎯

Event Delegation

Scale
Click any rowACTION
Single handlerACTION
Handles 1000+ rowsACTION
// One handler for unlimited rows
table.addEventListener("click", (e) => {
    const row = e.target.closest("tr");
    if (!row) return;
    
    const id = row.dataset.accountId;
    if (e.target.matches(".edit-btn")) {
        openEditor(id);
    }
});

JavaScript Runtime Visualized

Understanding how JavaScript executes code is essential for debugging and performance optimization.

Call Stack Animation

main()waiting
fetchAccounts()waiting
validateResponse()waiting
transformData()waiting
renderDashboard()waiting

Event Loop Simulation

Call Stack
Task Queue
setTimeout callback
click handler
fetch callback
Microtask Queue
Promise.then()
queueMicrotask()

JavaScript Delivery Library

Browse a curated library of interaction playbooks, QA-ready checklists, and delivery templates.

6 modules available
JAVASCRIPTFoundations

DOM Manipulation Essentials

Master selecting, creating, and modifying DOM elements without frameworks.

45 minFundamentals
DOMquerySelectorvanilla-js
JAVASCRIPTIntermediate

Async Patterns & Promises

Handle asynchronous operations with Promises, async/await, and error boundaries.

60 minAsync Programming
promisesasync-awaitfetch
JAVASCRIPTAdvanced

State Management Patterns

Build predictable state containers without external dependencies.

90 minArchitecture
statereducersobservers
JAVASCRIPTIntermediate

Event Handling Deep Dive

Delegation, bubbling, capturing, and custom events for scalable UIs.

50 minEvents
eventsdelegationcustom-events
JAVASCRIPTAdvanced

Performance Optimization

Debouncing, throttling, virtual scrolling, and memory management.

75 minPerformance
performancedebouncememory
JAVASCRIPTFoundations

Form Validation Patterns

Build accessible, real-time form validation with clear error messaging.

40 minForms
formsvalidationa11y