Senior Full Stack Developer (Node.js + React.js) – Debugging & Performance Optimization

@royalwebraisers

Hi, As per my understanding: you need a senior full-stack developer to debug production issues, fix duplicate transactions, and optimize API performance in your Node/React/Mongo setup. I will share my portfolio on your first message. * Root-cause debugging + logging improvements * API optimization, indexing, caching (Redis) * Concurrency fixes for duplicate data Queries: access to logs/monitoring? infra details? priority issues? I will be looking forward to hearing from you. Kindest Regards

@MWaqar5246

Hi, most production issues like freezes, duplicate records, and slow APIs usually come from deeper problems—race conditions, inefficient queries, or weak state handling not just surface-level bugs. I’ve worked on similar Node.js + React apps where stability and performance were critical, and I focus on fixing root causes, not temporary patches. Here’s how I’d approach your system: • Trace logins freeze and crashes using logs + profiling (frontend state + API flow) • Fix duplicate orders by addressing race conditions, adding proper DB constraints/transactions • Optimize APIs (query tuning, indexing, response shaping, optional caching like Redis) • Improve error handling, logging, and request flow between frontend/backend • Clean up critical parts of the codebase for long-term stability I keep changes minimal but effective so nothing breaks in production while improving performance. Availability: can start immediately Initial fixes + audit: 2–4 days (depending on codebase size) Quick question: do you currently have any logging/monitoring in place (e.g., Winston, Sentry), or should I set that up as part of the process? If you need someone who can quickly step in, diagnose accurately, and stabilize the app without guesswork, I can help. Best regards, M Waqar Tariq

@ashinnd84

Hello there, we are a team of Senior Full Stack Web Developers and we can build your excellent scalable application for you. Please, send me a message to discuss the work and finish in no time. Thanks Ashish Kumar.

@nitinjohnson316

Hello, This looks like a mix of race conditions, inefficient queries, and unstable state handling between API and client. Duplicate orders usually come from missing idempotency or concurrent writes I have fixed this using atomic operations and request guards. Login freezes and crashes often trace back to blocking calls or unhandled async errors. Slow APIs (2–5s) are typically Mongo query/index issues or N+1 patterns. I will reproduce issues in a controlled setup - trace logs + DB ops - fix root causes (not patches) - add safeguards (transactions, indexing, caching where needed). I have handled similar production apps where stabilizing reduced error rates and cut API times below 500ms. Regards, Nitin Johnson

@HemantManglani01

Hi there, I'm Hemant, a Senior Full Stack Developer with over 6 years of experience specializing in Node.js, React.js, and MongoDB. I’ve spent my career tackling complex production issues, optimizing performance, and bringing stability to live applications, much like yours. Your project, with its app freezes, duplicate orders, and slow APIs, sounds exactly like the kind of challenge I thrive on. I excel at quickly diving into existing codebases, pinpointing root causes, and implementing robust, scalable solutions to ensure a smooth user experience. My focus is on delivering clean, maintainable code that directly addresses your current performance and stability issues. I'm confident I can get your mobile app back on track. Let's chat more about your specific needs. Best, Hemant

@pheonixsolutions

Hi, This is something we can step into quickly. At Pheonixsolutions, we’ve handled similar situations where a live app starts breaking under real usage. Issues like duplicate orders, slow APIs, and login freezes usually come down to a mix of backend logic, database handling, and missing safeguards. Review backend flow (especially order creation and transactions) to fix duplicate entries Check API performance, optimize queries, add indexing where needed Trace login freeze issue (likely async handling or API blocking) Fix crash points when fetching user data Add proper error handling and logging so issues don’t repeat silently Clean up communication between frontend and backend We’ve worked with Node, Express, React and MongoDB in production setups, so understanding an existing codebase and fixing issues won’t be a problem. For cases like duplicate data, we usually check for race conditions, missing validations, and lack of atomic operations. For slow APIs, it’s often query optimization, indexing, or caching that makes the difference. We can also suggest improvements like: Better request handling Basic caching (Redis if needed) Safer authentication flow Cleaner structure for long-term stability We’re available to start immediately and can give quick turnaround on critical fixes first, then move into deeper optimization. Happy to share similar debugging work we’ve done. Let us know ? Thanks Pheonixsolutions

@utsav007pandya

I can stabilize your live app fast and eliminate the root causes behind crashes, duplicates, and slow APIs. With 6+ years in Full Stack (Node.js, React, MongoDB), I specialize in debugging production systems, optimizing performance, and implementing clean, scalable fixes. I’ll audit the codebase, resolve concurrency issues, improve API speed, and strengthen error handling/logging. Clear updates and maintainable code guaranteed. Let’s fix your app and make it production-strong—ready to begin immediately.

@AliMhenterprise

Hi, I hope you're doing well. Production debugging on Node.js/MongoDB stacks — not greenfield work — is where I'm most effective, and the issues you've listed are diagnosable patterns I've resolved before. The duplicate orders problem points to a race condition or missing idempotency key on the order creation endpoint — fixable with atomic MongoDB operations or a Redis-based lock. The 2–5 second API responses typically trace to unindexed queries or missing pagination — a quick `explain()` audit on your slowest endpoints usually surfaces the culprit fast. Login freezes in React Native most often come from unresolved promise chains or a blocking auth middleware call. I'd instrument all three with proper logging before touching any code so fixes are confirmed, not guessed. My debugging approach on live systems: reproduce in staging first, add structured logging to isolate the exact failure point, fix with minimal blast radius, verify in production with monitoring in place. No blind patches on live apps. Redis caching for repeat API calls, JWT hardening, and rate limiting I'd layer in alongside the bug fixes — they're quick wins that compound the performance improvement. Availability: immediate. Turnaround on initial fixes: 3–5 days depending on codebase size. Can I ask — do you have any existing logging or monitoring in place (Datadog, Sentry, Winston logs), or is visibility into production errors currently limited? Best regards, Syed Muhammad Ali Farhan

@amit210279

Hi there, You’re in the RIGHT PLACE! I’ve worked on SIMILAR PROJECTS multiple times and understand how to deliver this EFFICIENTLY and CORRECTLY from the start. While I’m NEW to Freelancer.com, I bring 17+ YEARS OF EXPERIENCE from other freelancing platforms, successfully delivering HIGH-QUALITY PROJECTS and REAL RESULTS for clients. To provide an accurate SCOPE, TIMELINE, and COST, I’d like to ask a few KEY QUESTIONS. Due to Freelancer’s character limit, it’s difficult to cover everything here. Let’s connect in CHAT so I can: • Share RELEVANT PAST WORK • Understand your EXACT REQUIREMENTS • Propose a CLEAR and EFFECTIVE ACTION PLAN I’m confident you’ll find my approach PRACTICAL, TRANSPARENT, and RESULTS-DRIVEN. If you're ready to get this done the RIGHT WAY, I’d be happy to get started. Looking forward to CONNECTING with you. Best regards, Amit Ranjan

@lokeshn30

Hi, This is exactly the kind of production debugging and stabilization work I handle regularly. I have solid experience with Node.js, Express, React, and MongoDB, especially fixing live app issues under real user load. My Approach: I start by replicating issues in a controlled environment, then use logging and profiling to identify root causes. Login freeze → check API bottlenecks, auth flow, and state handling Duplicate orders → likely race conditions / missing idempotency / DB constraints Slow APIs (2–5s) → query optimization, indexing, and possible caching (Redis) Crashes → error boundaries, null handling, and API response validation I focus on permanent fixes, not temporary patches. What I’ll deliver: • Debugged and stabilized frontend + backend • Optimized MongoDB queries & API performance • Fix for duplicate data issues (with proper safeguards) • Improved error handling, logging, and code quality • Clear documentation of fixes and recommendations Availability: I can start immediately and deliver initial fixes within 3–5 days, followed by deeper optimization if needed. Experience: I’ve worked on multiple live production apps, resolving performance issues, scaling APIs, and stabilizing systems with similar stacks. If you share access, I’ll begin with a quick audit and outline priority fixes within hours. Let’s get your app stable and running smoothly.

@oimrqs

I can take a focused first stabilization pass on this codebase and keep the output reviewable. I would start by reproducing the login freeze, duplicate order/transaction path, slow API calls and user-data crash, then add temporary logging around the failing endpoints/components to isolate root causes. Likely checks: duplicate submit/race conditions, missing idempotency guards, Mongo indexes/query shape, unhandled async errors, frontend retry/loading states and API timeout handling. For this bid I am proposing a compact debugging pass with clear change notes: what was reproduced, what was fixed, what was measured before/after, and what should be handled next. Text updates in Freelancer chat work for me.

@meharb34

Sparta Tech – High-Performance AI & Web Solutions Sparta Tech is a state-of-the-art digital agency website designed to showcase premium AI and automation services. The client's goal was to have a website that looks like the 'future of technology'—something ultra-modern, dark-themed, and highly interactive. Key Features: 1. Luxury UI/UX with Neon-Cyan aesthetics. 2. Interactive 'What We Do' sections for AI Dev and Data Analytics. 3. Fully SEO-optimized structure with clean, maintainable code. 4. Fast-loading performance with optimized technical assets.

@henryc484

Hello ✨ I’m interested in helping stabilize your live mobile application. I’ve worked with Node.js, Express, React, and MongoDB in production environments, and I’m comfortable stepping into an existing codebase to quickly find root causes and fix issues cleanly. My debugging approach starts with tracing the issue from the user symptom through logs, network requests, backend logic, and database behavior, then verifying the fix with testing and monitoring. For problems like login freezes, duplicate orders, slow APIs, and crashes when fetching user data, I focus on race conditions, query performance, state flow, and error handling. ✅ I’ve also handled production issues by improving MongoDB queries and indexes, using atomic updates where needed, tightening validation, and reducing unnecessary backend work. That helps improve stability, response times, and overall user experience. I can start quickly, communicate clearly, and provide brief documentation of the fixes and improvements once the application is stable.

@umeshkumary2

I will debug and stabilize your Node.js, React, and MongoDB app by fixing duplicate data issues, optimizing slow APIs, resolving crashes, and improving overall performance with clean, scalable code and proper error handling.

@arshkumar213

I am a senior **Full-Stack Engineer (3+ years)** specializing in stabilizing production-grade **MERN** stacks. I will systematically eliminate your app's crashes and race conditions using elite debugging and performance tuning. **My Plan:** * **Optimization:** Tuning **MongoDB** indexing and optimizing **Express** middleware to slash API latency from seconds to milliseconds. * **Integrity:** Solving duplicate orders by implementing **idempotency keys** and **database transactions** to handle concurrency. * **Stability:** Debugging the login freeze and fetching crashes using **React** profiling and comprehensive **Winston/Morgan** logging. * **Security:** Strengthening **JWT** flows and rate-limiting to ensure a production-hardened environment. **Turnaround:** Immediate availability for high-priority fixes. Ready to stabilize!

@mohjamit31084

We have been developing web and stand alone application with two decade of experience. Working on SAAS projects and handling full stack development.

@subhashswarnkar

Hi I am subhash swarnkar I have good experience in full stack and app development on react js , delivered 3 highly scalable apps for the startups. And In full stack more than 10+ web apps i delivered

@krishnawat

Hi, I’m a Senior Full Stack Developer (8+ years) experienced with Node.js, Express, React, and MongoDB, and I specialize in fixing production issues. I can quickly identify and resolve your current problems—login freezes, duplicate orders, slow APIs, and app crashes—by addressing root causes like race conditions, inefficient queries, and poor error handling. I’ve previously improved API performance by up to 70% and stabilized apps facing similar issues. I can start immediately and deliver a stable, optimized solution within a few days

@archnasardhara9

Hi, I have 7+ years of experience with Node.js, React.js, and MongoDB, and I specialize in debugging and optimizing live production applications. I can quickly identify and fix issues like login freezes, duplicate orders, slow APIs, and app crashes, while improving overall performance and stability. My approach includes code audit, performance tuning, fixing race conditions, and enhancing error handling. I’m available to start immediately and can deliver quick fixes followed by optimization. Let’s connect to discuss your project. Best regards, Archana