Expert Developer for Reengineering and Bug Fixing in Javascript Web Applications

Budget: 250 EUR Deadline: 5 days

Hi Mario. I've cleaned up a couple of AI-written Vanilla JS apps sitting on Supabase — in my experience the random freezes usually come from realtime channels that get re-subscribed on every render and never closed, plus fetches with no abort or timeout, so one slow request blocks the whole screen. Before touching the code I'd go through your Supabase and Upstash logs and reproduce one freeze, otherwise it's guesswork. Do the hangs show up on a specific screen, or anywhere once the tab has been open for a while?

Budget: 650 EUR Deadline: 5 days

I can take this as a technical stabilization and reengineering task, but 250 EUR is likely only enough for a limited diagnostic pass. For a real first stage with bug reproduction, log analysis, root cause mapping, and critical fixes, I would estimate from 650 EUR and 5 working days.

WE would start with Supabase, Upstash and Vercel logs, then reproduce the freezes, isolate whether the problem is state handling, realtime subscriptions, queries, Redis usage, or frontend async flow. After that I would patch the highest risk parts - loading states, failed requests, retries, state persistence, and secure API usage. I would probaly avoid a large rewrite first, because stability issues need evidence before surgery =/

> Please share whether the app has a repository with reproducible steps for the crashes.
> Do the freezes happen for all users or only after login, realtime updates, or specific database actions?

Relevant examples from Ingello
> https://business.ingello.com/fractal - close by architecture and complex software logic with AI assisted systems
> https://business.ingello.com/platforma - relevant to platform stability, roles, data flows and business logic
> https://business.ingello.com/vorfahr - related to SaaS and automation product development

Main Ingello FLH page - https://systems-fl.ingello.com

!!Important point!! - I would treat this as an engineering audit plus critical stabilization, not as random bug fixing. Measure twice, cut once - boring wisdom, but here it saves budget and nerves. Expand

Budget: 250 EUR Deadline: 3 days

Hi.

I'm an experienced full-stack developer with ten years under my belt. I've worked on large-scale projects such as ride-hailing (online taxi marketplace), express delivery, and hypermarket&delivery platforms.

I'm feel confident working with someone else's code — finding and fixing bugs, and improving the codebase through refactoring. This is what I deal with on a daily basis, so if you're looking for someone you won't have to worry about when it comes to quality and results — reach out, let's talk through your project. I'll run a proper audit of the current codebase, and together we'll map out a plan for how to move forward and hit your goals.

As for bugs: over all my years in IT, I've become convinced that solid error detection at the architectural level — together with proper handling, logging, and monitoring — takes away that pain and dramatically speeds up both incident response and the development process itself.

Yes, I understand the code was generated by AI — but I've come across code from indie developers where, honestly, the AI comes out ahead.

I've worked with JavaScript from the very start web experience, so I've walked the not-so-easy road from Native JS, jQuery, and Angular all the way to React and Vue.js. So that's no problem for me at all. Expand

Budget: 250 EUR Deadline: 5 days

Hi Mario,

Intermittent freezes in an AI-generated Vanilla-JS app usually trace back to unhandled async states around the data layer: a Supabase Realtime channel that silently drops and never reconnects, or an Upstash/Redis call with no timeout that hangs and leaves the UI stuck loading. That lines up with the "periodic crashes and hangs in certain features" you describe.

How I'd approach it:
- Reproduce and instrument first: pull the Supabase and Upstash logs, correlate them with the frontend network errors, and pin the real root cause instead of patching symptoms.
- Harden the async paths: proper loading/error handling, request timeouts and reconnect logic for Realtime and Redis, so a dropped connection recovers instead of freezing.
- Tighten state and queries: fix stale frontend state, cut redundant round-trips, and keep the API calls safe (no keys exposed client-side).

I work with modern JS, PostgreSQL and Redis daily and I'm comfortable reading through AI-generated modular code. The price fits your 250 EUR budget; a realistic timeline is 4-5 days once I have repo access and can see the logs.

One question to scope this precisely: are the freezes tied to specific actions (login, realtime updates) or do they happen randomly across the app?

I'm taking on my first projects here to build up reviews, so you get senior-level attention at this price. Happy to do a quick screen-share of the diagnosis before I touch any code.

Petro Pankov, BotCraft Group Expand

Budget: 250 EUR Deadline: 5 days

Hello Mario,

Intermittent freezes in a Vanilla JS app on Supabase Realtime plus Upstash Redis almost never come from the feature that visibly hangs. In my experience the usual root causes are:

- Realtime subscriptions that are created on every re-render or route change and never unsubscribed, so after a while the client holds dozens of open channels and the socket starts backing up.
- No reconnect/backoff handling: Supabase drops the websocket (tab sleep, network blip), the app never resubscribes, and the UI just sits there looking "stuck".
- Redis calls issued per keystroke or per scroll event instead of being debounced, hitting Upstash rate limits — which return errors that the app swallows silently.
- Serverless cold starts on Vercel masked as "the app froze".

How I would work:
1. Reproduce first. Instrument the client: log every channel subscribe/unsubscribe with a counter, wrap every Supabase and Upstash call to record latency and errors. Without a reproduction, any fix is a guess.
2. Read the network waterfall and Vercel function logs around the exact moment of the freeze, not in general.
3. Fix root causes, not symptoms — and tell you plainly which ones I found and which I could not confirm.
4. Regression check: a short script that drives the problem flows repeatedly, so the freeze cannot come back unnoticed.

What I need from you: repository access, Supabase and Vercel project access (read-only for logs is enough to start), and one concrete example — which feature hangs, how often, and roughly when it last happened.

About me: I build and run autonomous systems in production 24/7 on Linux VPS — Python, Node, systemd, monitoring, self-restart. Debugging someone else's code, reading logs and stabilising "almost working" systems is exactly what I do. Playwright and Puppeteer are daily tools, so the regression harness is not extra work for me.

My work: guardlabs.online/studio

Bid: 250 EUR, 5 days. If the root cause turns out to be smaller than it looks, I will say so and we can cut the scope — I would rather keep the estimate honest than pad it.

Note: the project description was auto-translated on my side, so if I misread any requirement, correct me and I will adjust. Expand

Budget: 250 EUR Deadline: 1 day

Hello.I have been working with JavaScript for more than 9+ years. I'm ready to cooperate.

Budget: 21750 EUR Deadline: 8 days

Hi Mario,

This is exactly the kind of project where a careful human review matters more than rewriting everything.

Your app already works, which usually means the real issue is not “bad code” overall, but unstable logic around async flows, state persistence, network failures, and service communication. In Vanilla JS apps, intermittent freezes often come from unhandled promise chains, race conditions, inconsistent local state, or weak recovery when Supabase/Upstash requests fail or return later than expected.

I can help by approaching this in the right order:
- inspect the failing flows using Supabase and Upstash logs, plus browser/network behavior
- isolate the exact crash/freeze triggers instead of masking symptoms
- refactor the affected JS modules to make loading, error, retry, and empty states explicit and safe
- review frontend state persistence so the UI cannot drift into broken or stale states
- improve request handling with Supabase/Upstash for better reliability, cleaner query flow, and safer integration
- keep the existing modular structure where it makes sense, while strengthening the parts that are currently fragile

I’m comfortable working in pure ES6+ JavaScript without relying on frameworks, and I understand the extra discipline that requires in state handling and async control. I also like that you mentioned the code was AI-assisted: that usually means the structure is usable, but edge cases and failure handling need experienced review.

If you want, I can start with a focused diagnosis of the most unstable functionality first, then move into targeted refactoring so fixes are measurable and low-risk.

🌐 My portfolio with recent cases:
https://mrnko.com
💼 Freelancehunt profile:
Freelancehunt
🤝 I’ll be glad to discuss the details, answer your questions, and suggest the optimal solution for your project. Expand

Budget: 250 EUR Deadline: 2 days

Hello. Mario M.
I have extensive experience working with JavaScript and Supabase.
In particular, I have specific experience with Supabase Edge Functions, RLS, and authentication.
I have carefully reviewed the requirements of your project, and as you can see in my portfolio, I have significant experience in the areas you are requesting.
I look forward to the opportunity to discuss this in more detail in the future.
Thank you.

Budget: 250 EUR Deadline: 3 days

Hi Mario,
I'm Hiroshi Funaoka from Japan.
I have a look at your post carefully.
I can do it perfectly.
Looking forward to our discussion. thank you!

Budget: 250 EUR Deadline: 7 days

Hello, I worked on a Dashboard for a startup — refactoring Vanilla JS + Supabase realtime, reduced the number of crashes by 80% and the API response time from 2s to 400ms.

Mario, I'm curious to know — does the app crash more often with simultaneous realtime subscriptions from multiple users, or is it more related to specific operations in Supabase/Redis?

I suggest we connect, I will provide you with free technical consultation and we can create a development plan + I will tell you about my team!

Budget: 250 EUR Deadline: 1 day

Hello, Mario!
The overall task is clear. To give you a precise answer regarding timeframes and pricing, I'd like to clarify a few questions I had after analyzing your task.
Privately message me – we'll discuss the details and your preferences.

Budget: 465 EUR Deadline: 21 days

I have experience working with JavaScript, API integrations, and databases. I can conduct a code and log audit, localize the causes of freezes, fix error handling and states, optimize queries to Supabase/Upstash, and prepare the application for stable operation on Vercel. Please advise:
1. Is there access to the repository, Vercel, Supabase, and Upstash?
2. Which specific functions most frequently freeze or crash?
3. Are there logs, screenshots of errors, or a stable reproduction scenario for the issue?
4. How large is the project code and is there documentation on the architecture?
5. Is only fixing critical bugs needed or also a complete refactor of individual modules?
6. What are the desired timelines and is there any planned support after the fixes?

Budget: 900 EUR Deadline: 10 days

Good morning,

You wrote something that is the most important in this announcement: the code was created with the help of Claude Code, has a reasonable modular structure, but needs human verification to be truly robust. This is exactly the model we work with every day — the code is written by AI, and an experienced engineer is responsible for every line that goes into production.

From the described stack (Vanilla JS + Supabase Realtime + Upstash + Vercel) and the symptom of "occasional freezes of selected functions," there are three most common causes from which I will start the diagnosis:

1. Realtime channels that are not unsubscribed when changing views, and lack of reconnection after a WebSocket disconnection — the application appears to be alive but stops receiving events. The symptom is random, as it depends on the user's network.
2. Lack of uniform handling of loading states and errors — unhandled promise rejection leaves the interface in a state of "eternal loading." This is usually the source of "freezing," which does not leave a clear trace in the logs.
3. Upstash: query limits and lack of exponential backoff — under load, individual requests quietly fail.

Plan: first, two days for analyzing Supabase/Upstash logs and reproducing the failure (production events plus load testing), then a list of causes with priorities for your approval, and only then refactoring — a common data access layer with retrying and interrupting requests, one mechanism for loading and error states, and organized state persistence on the front end.

How I work: price and deadline known before starting, payment for a functioning, tested result. Before acceptance, you will receive a video recording showing the failure before and after the fix — that is, proof that the cause has been removed, not just the symptom masked. The code goes to your repository.

The amount of 900 USD is the starting price — for the scope of "diagnosis plus fixing causes plus refactoring the data layer." I will provide a binding estimate after access to the repository and the Supabase project; if the scope turns out to be smaller, the amount will go down.

Best regards,
Adam — ALEA Systems Expand

Budget: 250 EUR Deadline: 4 days

WE already have a very close technical recovery pattern for vanilla JavaScript, Supabase, Upstash and Vercel, so i can adapt it very quickly and discuss the first checks here now - i am online ))
for 250 EUR i can do a focused stabilization phase in 4 days - reproduce crashes, read Supabase and Upstash logs, isolate network and state failures, then patch the most critical places.
the goal is stablity first, then performance.
i would check loading and error states, frontend persistence, Realtime subscriptions, Redis calls, query efficiency, Vercel variables and browser console traces.
from you i would need repository access, Vercel access, Supabase and Upstash logs, plus 2-3 exact user flows where freezes happen.
question 1 - are the crashes tied to Supabase Realtime subscriptions or do they also happen on simple page navigation.
question 2 - is there any recent deployment after which the instability became visible.
https://business.ingello.com/fractal - relevant because it shows our work with complex logic, automation and system reliability.
https://business.ingello.com/platforma - close to business software stabilization and architecture cleanup.
https://systems-fl.ingello.com - main Ingello Systems page for Freelancehunt projects.

Budget: 250 EUR Deadline: 2 days

Hello, Mario!
The symptoms you described periodic crashes and freezes in specific functions are classic issues for modular Vanilla JS applications developed with AI assistance. While AI is excellent at structuring logic, it frequently misses the architectural nuances of asynchronous data streams, memory management, and state handling.

Budget: 250 EUR Deadline: 3 days

Hello!

I am ready to quickly join the project, find the causes of periodic freezes, and stabilize the operation of your application. I have extensive experience working with pure JavaScript (Vanilla JS) and optimizing the performance of web applications.

Budget: 1234 EUR Deadline: 1 day

Hello! I have experience working with Vanilla JavaScript, bug fixing, and code optimization, as well as integration with Supabase and APIs. I would be happy to help you!

Budget: 250 EUR Deadline: 7 days

Hello! I am Volodymyr, a full-stack developer and the founder of the Vaysed engineering agency. I have reviewed your project requirements for debugging and re-engineering your Vanilla JS web application, and the task is absolutely clear to me.

Working with ES6+ JavaScript, Node.js, and complex backend architectures is my core expertise. I frequently deal with optimizing and refactoring AI-generated codebases. While tools like Claude write good logical structures, they often fail to implement robust state management and proper race condition handling in Vanilla JS, which is exactly why your application is experiencing intermittent crashes and UI freezes.

To resolve these critical bugs, I will start with a thorough audit of your Vercel deployment logs and analyze the communication between the client, your PostgreSQL database on Supabase, and the Redis cache on Upstash. Without a framework to handle state automatically, I will manually refactor your JavaScript to ensure that all asynchronous data fetching, loading states, and error handling are strictly controlled. I will also optimize your Supabase real-time subscriptions and query structures to eliminate bottlenecks and ensure secure API integration.

My engineering background guarantees that your application will not only be fixed but properly structured for long-term stability and high performance. You can review my approach and previous projects in my portfolio at Freelancehunt. I would be glad to get access to your codebase and discuss the specific error logs to provide a precise timeline and budget for this project.

Budget: 250 EUR Deadline: 5 days

Hi Mario,

Intermittent crashes and freezes in a vanilla JS app on Supabase Realtime usually trace back to a small set of causes, and the fact that the code was AI-generated makes them more likely rather than less. I work with AI-assisted code daily, including Claude Code, so I know where it tends to be structurally clean but operationally fragile.

The usual suspects I'd check first:
- Realtime channels subscribed but never unsubscribed, so subscriptions accumulate on navigation until the tab freezes
- Unhandled promise rejections, which crash silently and leave the UI stuck in a loading state forever
- Race conditions between concurrent queries, where a slow response overwrites a newer one, with no AbortController on navigation
- Upstash Redis called from the browser, which both exposes the token and invites rate-limit storms. That belongs behind a Vercel serverless function
- Missing or misconfigured RLS on Supabase, which turns into intermittent failures that look random

My approach: start with the actual evidence, network errors, Supabase and Upstash logs, and reproduce the freezes before touching code. I'd rather find the root cause than patch symptoms. Then refactor the loading and error handling into explicit states with retries and proper cleanup, consolidate frontend state into a single source of truth instead of scattered globals, and tighten the query and API layer.

Deliverable: a written diagnosis of each failure, what caused it, and the fix, plus the refactored code.

My stack: JavaScript and TypeScript, PostgreSQL, Supabase, Vercel. Track record: 37 projects, all completed, 10/10 rating.

250 EUR for the diagnosis and fixes stage, about 5 days. If the analysis shows a deeper structural refactor is warranted, I'll tell you before doing it rather than quietly expanding scope.

One question: are the freezes reproducible on demand, or do they only appear in production under real usage? That decides whether I start from logs or from a reproduction. Expand

Budget: 250 EUR Deadline: 4 days

I see your task regarding the stabilization of a web application on Vanilla JS with Supabase and Upstash. I will focus on log analysis, refactoring JS for reliable error handling, and optimizing state and communication with services.

Write to me, and we can discuss everything in detail, and I can start working right away.

Portfolio: Freelancehunt
Reviews: Freelancehunt

Budget: 250 EUR Deadline: 4 days

Hello Mario,

Your description strongly suggests the application doesn't need to be rewritten. The most likely causes are race conditions, duplicated Realtime subscriptions, unfinished async operations, or inconsistent frontend state after network failures.

My approach is to identify the root cause first instead of patching symptoms. I'll analyze Supabase and Upstash logs, inspect network requests, reproduce the failing scenarios, and determine exactly what triggers the crashes and freezes. After that, I'll refactor only the affected modules while preserving the existing architecture where it already works well.

I'll also review loading and error state handling, frontend state persistence, Realtime subscriptions, duplicate requests, async flow management, query efficiency, and the integration between the client, Supabase, and Upstash. If the issue involves Auth, RLS policies, or state synchronization, I'll verify those as well.

As a first step, I can review one problematic workflow or one module at no cost and provide my findings on the most likely source of the instability. If you're satisfied with the analysis, we can continue with the complete refactoring.

My rate starts at 250 EUR. The final estimate will depend on how many modules require refactoring after the initial diagnosis, since intermittent issues often have multiple underlying causes rather than a single bug. Expand

Budget: 250 EUR Deadline: 5 days

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Let’s collaborate and create something amazing together! Expand

Budget: 250 EUR Deadline: 3 days

Hello, Mario! My name is Nina, I am a manager. We have thoroughly understood the problem with your application. The situation is classic: AI (Claude Code) writes modular Vanilla JS structure well, but often makes mistakes in complex asynchronous operations (race conditions), handling edge cases, and memory leaks during Realtime subscriptions.

My Full-Stack developer works daily in the Claude / Vercel / Supabase ecosystem and will quickly find the root of the problem.

How he will solve the task:
Log analysis: He will study network requests, Vercel Functions logs, and limits in Upstash Redis to understand where the connection is hanging.
Fixing asynchronous issues: He will rewrite promise chains, add strict error handling (try-catch), loaders, and protection against duplicate API requests.
Database optimization: He will check Supabase Auth sessions and Realtime listeners (they need to be properly closed to prevent the application from hanging).

The engineer works quickly directly through the CLI terminal, and the code will remain clean and free of unnecessary libraries. Please message me, ready to discuss the details.
Cost: 250 EUR
Deadline: 3 days Expand