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I will migrate your react javascript modules to typescript
Jonathan G
About this gig
Ready to improve your React codebase with TypeScript? I will migrate a clearly defined set of JavaScript modules while preserving their agreed behavior.
I have hands-on experience migrating a substantial production application from JavaScript to TypeScript in a financial-services team.
Basic: up to 3 files and 600 nonblank source lines.
Standard: up to 10 files and 2,000 nonblank source lines.
Premium: up to 20 files and 4,000 nonblank source lines.
Both limits apply, with a maximum of 200 nonblank lines per selected file.
You receive typed source code, appropriate props and data types, configuration changes where needed, verification notes and a migration handover. I document any unavoidable typing exceptions.
Please send your stack, file list and current build status before ordering so we can agree the migration boundary. The application must run before migration.
Framework upgrades, new features, runtime API validation and whole-app strict-mode cleanup are excluded. Large or tightly coupled projects need a custom scope.
Get to know Jonathan G
Jonathan G
React Nextjs and TypeScript Developer
- FromGermany
- Member sinceAug 2019
Languages
English, German, Chinese, Korean
I'm Jonathan, a German fullstack developer with 4+ years of professional experience in agency and financial-services teams. I build and maintain web applications with React, Next.js and TypeScript. I can help you fix frontend bugs, connect Sanity CMS, migrate JavaScript to TypeScript, or build a document chatbot with source citations. You receive maintainable code, testing notes and a clear handover. I work in German and English and am based in South Korea. Send me your requirements so we can agree on a practical scope.
Other Software Development Services I Offer
FAQ
How are migration limits calculated?
Basic: 3 files/600 lines; Standard: 10 files/2,000 lines; Premium: 20 files/4,000 lines. Both limits apply, with 200 nonblank lines maximum per file. Shared source changes count; configuration, lockfiles and generated files do not.
Will you migrate my entire application?
Only if the entire reviewed application fits a listed package. Most orders cover one module. Tightly coupled or larger codebases need a staged custom offer after reviewing dependencies.
Will you just rename files or add any everywhere?
No. I add meaningful types and record any unavoidable third-party exceptions. Whole-app strict mode is not included. External API payloads receive compile-time types; runtime validation is a separate deliverable.
What testing is included?
I run scoped type checks, the existing build and relevant existing tests, plus 1, 2 or 4 agreed behavior checks by tier. Those checks use your existing harness where suitable, otherwise repeatable manual steps. A new full test framework is excluded.
Can you migrate a broken project or upgrade Next.js too?
The project must run before migration. Existing unrelated errors, major package upgrades, architecture changes and React-to-Next.js migration need a separate scope.
What counts as a revision?
One revision is one consolidated feedback round on the agreed deliverable. It does not add pages, features or integrations. New scope needs a separate quote. Report defects in my delivered changes within 7 days of completion for correction; unrelated changes are excluded.
Do I receive source code and are ongoing costs included?
Source code and setup notes are included. Hosting, domains, paid assets, CMS plans and AI or other API usage are paid by you. Third-party libraries retain their licenses. Use your own service accounts; do not send passwords or secret API keys in chat.
Do you use AI development tools?
I may use AI coding tools to assist development, and I remain responsible for reviewing and testing the delivery. Tell me about AI restrictions before ordering. I will agree the handling of confidential code or documents with you before using external AI services.
How will we communicate?
I work in English and German and am based in South Korea. Please use Fiverr messages for project scope, updates and approvals. Repository access is only for delivery. Calls are by appointment through Fiverr where available, with a written handover as the default.
