Catch bugs before runtime
TypeScript catches type errors, null references, and API mismatches at compile time instead of in production. Research across large codebases shows a meaningful reduction in preventable defects after a JS-to-TS migration.
JavaScript to TypeScript Converter
Convert JavaScript to TypeScript – free, online, deterministic.
JavaScriptConverter turns .js into typed
.ts using deterministic AST transforms — not AI guesswork.
It rewrites CommonJS require/module.exports
as ES modules, pulls types out of JSDoc, lifts class fields, hoists static members,
and emits a ready-to-compile tsconfig.json in seconds.
JavaScript to TypeScript conversion preview
INPUT — app.js
const express = require('express');
/**
* @param {string} name
* @returns {string}
*/
function greet(name) {
return 'Hello ' + name;
}
module.exports = { greet };OUTPUT — app.ts
import express from 'express';
/**
* @param {string} name
* @returns {string}
*/
function greet(name: string): string {
return 'Hello ' + name;
}
export { greet };- AST transform steps
- 8
- Determinism
- 100%
- Per-file conversion time
- <1s
- JavaScript syntax supported
- ES2024+
AST Transform Steps
Deterministic Output
Per-File Conversion
Syntax Support
Why Migrate to TypeScript
TypeScript is the industry standard for production JavaScript
Teams that migrate from JavaScript to TypeScript report fewer production bugs, faster onboarding, and stronger refactor confidence. The blocker is usually the manual rewrite — which is exactly what this converter automates.
Better IDE experience
Type information powers intelligent autocomplete, inline documentation, and jump-to-definition in VS Code, WebStorm, and every modern editor. TypeScript makes the whole codebase navigable.
Easier team collaboration
Type annotations act as living documentation. New engineers understand public APIs without reading implementation details, and code review focuses on behavior instead of shape.
Conversion Engine
What JavaScriptConverter actually does
Every transform is a deterministic AST operation — no LLM hallucinations, no random output. The same JavaScript input always produces the same TypeScript result.
File renaming .js → .ts
Renames .js to .ts and .jsx to .tsx with automatic JSX detection in file contents.
CommonJS require to ES import
require() becomes import — default, named, and destructured forms are all handled.
module.exports to ES export
module.exports becomes export default, and exports.x becomes a named export.
JSDoc to TypeScript types
Reads @param and @returns from JSDoc comments and inlines them as real TypeScript type annotations.
Class field detection
Detects this.x = ... assignments in constructors and generates typed class field declarations at the top of the class body.
tsconfig.json generation
Emits a tsconfig.json configured for your project's module system and strictness preferences.
Static property hoisting
Moves MyClass.prop = value assignments into the class body as static property declarations.
Private & protected inference
Infers private and protected modifiers from naming conventions like _underscore prefixes.
Error suppression scaffolding
Adds @ts-expect-error comments where residual TypeScript errors remain, so the converted project compiles immediately.
How It Works
How to convert JavaScript to TypeScript in 3 steps
Whether you start in the browser or the desktop app, the JavaScript-to-TypeScript workflow is identical and designed to minimize surprises.
-
1
Choose your workflow
Use the online converter for quick single-file jobs, upload ZIP files for batch conversion from the dashboard, or install the free desktop app for full project control.
-
2
Deterministic AST transforms run
The engine parses your code into an Abstract Syntax Tree with ts-morph and applies each conversion step predictably. No AI randomness — identical input always produces identical TypeScript output.
-
3
Download and refine
Download the converted TypeScript files with full diagnostics. Review the changes, tighten types where needed, and commit to your repository with confidence.
Every conversion tool in one place
Twenty-four free converters — framework migrations, runtime validation schemas, cross-language type emitters, and a mock-data generator. Pick the one that fits.
JavaScript → TypeScript fundamentals
Online JS to TS Converter
Paste JavaScript and get TypeScript back — the flagship tool. CommonJS, JSDoc, classes, exports.
Open converter ›CommonJS to ES Modules
Rewrite require() and module.exports to modern import / export.
JSDoc to TypeScript types
Promote @param and @returns comments into inline TypeScript type annotations.
JSON to TypeScript
Paste a JSON sample and get a TypeScript interface back. Runs entirely in your browser.
Examples Gallery
Twelve before/after pairs covering the patterns the engine handles — classes, JSDoc, Express, React.
Browse examples ›TypeScript to Zod
Generate a Zod runtime schema from a TS interface. Single source of truth via z.infer.
Frontend frameworks
React JSX to TSX
Detect JSX, rename to .tsx, type props and hooks.
Vue.js to TypeScript
Composition API and <script setup> with typed props and emits.
Angular to TypeScript
Migrate AngularJS 1.x services and controllers to typed classes.
Open guide ›Svelte to TypeScript
Runes, $props(), and SvelteKit load functions.
SolidJS to TypeScript
Type createSignal, stores, and async resources.
Preact to TypeScript
React-API-compatible components with jsxImportSource.
Schemas & runtime validation
TypeScript to JSON Schema
Emit Draft 2020-12 JSON Schema from TypeScript interfaces.
Open tool ›JSON Schema to TypeScript
Turn a JSON Schema into TS interfaces with $ref resolution.
OpenAPI to TypeScript
Tooling guide: openapi-typescript, openapi-fetch, orval, kubb.
GraphQL to TypeScript
SDL types and operations — GraphQL Code Generator, gql.tada, Houdini.
Open guide ›Mock Data Generator
Realistic JSON test fixtures from a TS interface, seeded for reproducibility.
Open tool ›TypeScript to JavaScript
Strip types client-side — interfaces, generics, enums, casts.
Open tool ›Cross-language type emitters
Python
TypedDict / Pydantic / dataclass
Go
structs with JSON tags
C#
records or classes
Rust
serde structs
Java
records or POJOs
Kotlin
data classes
Swift
Codable structs
Backend
Node.js to TypeScript
Migrate Express, Koa, or Fastify handlers with inferred Request / Response types and a Node-tuned tsconfig.
Generate tsconfig.json
Auto-detect module system, JSX, and target runtime to emit a tsconfig.json that compiles on the first try.
Migration Guide
Practical strategy for moving large JavaScript codebases to TypeScript — modes, tooling, CI gates, timelines.
Read guide ›Online converter or free desktop app
Start with the web converter for quick jobs. Move to the free desktop app when you need full project control or must keep code 100% on your machine.
Online Converter
- Paste JavaScript and convert instantly in the browser
- Upload a ZIP archive for batch conversion
- Dashboard with order history and downloads
- No installation required — runs in any modern browser
- Free tier available with no account required
Desktop App for Windows
Recommended- Drag and drop entire folders
- File tree with selective conversion
- Per-file progress and full diagnostics
- 100% offline — code never leaves your machine
- Free — no account needed
JavaScript to TypeScript FAQ
Answers to the questions we hear most often about migrating from JS to TS.
Is JavaScriptConverter an AI-based converter?
No. JavaScriptConverter uses deterministic AST (Abstract Syntax Tree) transforms powered by ts-morph. Every conversion is predictable and reproducible — the same input always produces the same output. There is no LLM or AI involved, which means no hallucinated types or invented code.
Will the converted TypeScript code compile without errors?
The converter produces valid TypeScript that mirrors your original JavaScript behavior. Where types can be inferred from JSDoc or default values, they are added automatically. Remaining untyped parameters will use implicit
any. Enable strict mode gradually and add types manually for complex areas.
What module systems are supported?
Both CommonJS (
require/module.exports) and ES Modules (import/export). The converter detects CommonJS patterns and rewrites them as ES Module syntax. If your code already uses ES Modules, it is preserved as-is.
Is my code sent to a server?
The online converter sends code to our server for processing. If your code must remain private, use the desktop app — it runs the same conversion engine locally and never transmits files over the network.
How is this different from just renaming .js to .ts?
Renaming files is only the first step. JavaScriptConverter also rewrites CommonJS
require/exports as ES Module syntax, extracts type annotations from JSDoc comments, detects undeclared class properties, and generates a tsconfig.json. This gets you much closer to a working TypeScript project than a rename alone.
Can I convert React JSX files to TypeScript TSX?
Yes. The converter automatically detects JSX syntax in
.js and .jsx files and renames them to .tsx accordingly. All import/export and type-inference transforms work the same way with JSX content.
Ready to Start?
Start your JavaScript to TypeScript migration today
Try the online converter for quick jobs, install the free desktop app for full projects, and upgrade to a paid plan only when you need batch uploads and API access.
