JavaScript development company
We write JavaScript and TypeScript across the whole stack, from browser interfaces in React, Vue or plain web components to Node.js services, and we modernize older codebases without stopping the product your customers use every day.
- Senior engineers · IST + EST overlap
- NDA on day 1
- 24-hour reply
- Projects shipped
- 50+
- Code ownership
- 100%
- Client rating
- 4.8/5
- First reply
- 24h
JavaScript engineering from browser to server
Krapton is a JavaScript development company that builds and maintains web front ends, Node.js backends and the tooling between them. JavaScript runs everywhere, which is both its strength and the source of most of its problems: one codebase may mix CommonJS and ES modules, several bundlers, jQuery plugins and a React island, with a node_modules tree nobody has audited. Our engineers bring that under control. New work is written in TypeScript with strict mode, built with Vite or the framework’s own toolchain, linted with ESLint flat config and tested with Vitest and Playwright. Existing JavaScript is migrated gradually using allowJs and JSDoc types, so you get type safety file by file without a freeze. On the server we use Node.js LTS releases with Fastify, NestJS or Express, and we consider Bun or Deno only where their runtime gains matter more than ecosystem maturity. JavaScript is not ideal for CPU-heavy number crunching or long-running data pipelines; there we recommend Go, Rust or Python services alongside it.
JavaScript development services
Front-end application development
We build interfaces in React, Vue or Svelte, or framework-free with web components where a widget must embed in other sites, with accessibility and Core Web Vitals checked per release.
Node.js APIs and services
REST and GraphQL APIs on Fastify, NestJS or Express, with schema validation through Zod, structured logging with Pino, background jobs on BullMQ and OpenTelemetry tracing from day one.
JavaScript to TypeScript migration
We add a tsconfig with allowJs, type the shared modules and API boundaries first, then tighten strictness one directory at a time while CI blocks new untyped code.
jQuery and legacy modernization
Legacy jQuery or Backbone screens are replaced one route or widget at a time, with characterization tests first, so behavior stays the same while the code underneath changes.
Build tooling and bundle size
We move webpack or Gulp builds to Vite or Rspack, split bundles by route, remove duplicate dependencies and set size budgets that fail CI when a library bloats the payload.
Dependency and supply-chain hygiene
Lockfiles are enforced, install scripts are reviewed, Dependabot or Renovate updates arrive in small batches, and packages are checked with npm audit and Socket before they reach production.
Why teams choose Krapton for JavaScript
Senior engineers, fixed scope, and code you own — the things agencies promise and rarely deliver.
Type safety end to end
Shared TypeScript types or Zod schemas describe data once for the browser, the API and the database layer, so a contract change shows up as a compile error.
Event loop awareness
Engineers know what blocks the Node.js event loop, move CPU work to worker threads or queues, and measure with --cpu-prof profiles and flame graphs before guessing at fixes.
Security at the boundaries
Input is validated at every entry point, output is escaped by default, Content Security Policy headers are set, and prototype pollution and ReDoS risks are covered in review checklists.
Framework choice without dogma
We recommend React, Vue, Svelte or plain JavaScript based on your team, hiring market and product, and we explain what each choice costs you in maintenance later.
How a JavaScript project runs with Krapton
01
Codebase health check
We map modules, bundlers, runtime versions and dependencies, run the test suite, and list risks such as unmaintained packages or blocking synchronous code.
02
Target architecture
We agree the framework, module format, TypeScript strictness and testing approach, and document them as short decision records in the repository.
03
Incremental delivery
Features and refactors ship in small pull requests behind flags, with unit tests in Vitest and end-to-end checks in Playwright gating each merge.
04
Observe and maintain
Sentry, OpenTelemetry and real user monitoring report errors and slow interactions after release, and dependency updates continue on a fixed cadence.
The JavaScript stack we build with
JavaScript development: questions answered
What kind of projects does a JavaScript development company take on?
Almost anything that runs in a browser or on Node.js. Typical projects are customer-facing web apps, admin dashboards, embeddable widgets, browser extensions, REST or GraphQL APIs, real-time features over WebSockets, and serverless functions. Just as often the work is remedial: untangling a legacy jQuery front end, moving a codebase to TypeScript, speeding up a slow single-page app or replacing an abandoned build setup.
Should new projects use JavaScript or TypeScript?
TypeScript, for almost any codebase that more than one person will maintain. It catches contract mismatches at build time, makes refactoring safer and documents APIs in the editor. Plain JavaScript still makes sense for small scripts, quick prototypes and some library code that ships JSDoc types instead. Since TypeScript compiles to JavaScript, the runtime behavior and performance are the same either way.
How do you modernize a legacy jQuery application?
Gradually, by replacing one screen or widget at a time rather than rewriting everything. We first write Playwright tests that record current behavior, then mount new React, Vue or web component islands inside existing pages, sharing state through events or a small store. Old plugins are removed as their screens move over, and the build is moved to Vite so new and old code ship from one pipeline.
How do you make a slow JavaScript app fast?
By measuring first, because the cause is usually specific. In the browser we look at bundle size, long tasks and Interaction to Next Paint, then code-split routes, defer third-party scripts and move heavy work to Web Workers. On Node.js we profile the event loop, fix N+1 database calls, add caching and stream large responses. Each change is verified against the same metrics before and after.
What affects the cost of JavaScript development services?
Scope, starting point and quality bar affect it most. Building new on a clean stack differs from working inside a large legacy codebase with no tests. Other drivers are the number of integrations, real-time or offline requirements, accessibility and compliance targets, browser and device support, the amount of TypeScript migration or refactoring needed, and the mix of senior and mid-level engineers the work calls for.
Ready to build? Tell us what you have in mind.
Send a short brief and a senior engineer will reply within one business day with next steps — no sales fluff.