Js2ts

JS2TS is a free online tool that converts JavaScript code into TypeScript using AI. You paste your JavaScript, click Convert and get TypeScript with interfaces, generics and type annotations added. It needs no login, and the site positions it as a way to reduce the manual work of migrating a codebase to TypeScript.

How to use it

Type or paste JavaScript into the input box, either written directly or copied from your editor. Click Convert, and the converted TypeScript appears in the output box. There is also a sample code button if you want to see how the conversion works first, and the page includes worked examples such as converting a simple function.

Other converters

Beyond the main tool, the site offers a wide set of developer converters. TypeScript tools include JSON to TypeScript, TypeScript to JavaScript, TypeScript to Zod and OpenAPI to TypeScript. Data tools cover JSON to Zod, JSON Schema, YAML, CSV, SQL, Markdown, BigQuery and Go, plus YAML, XML and CSV to JSON. CSS and HTML tools convert CSS to Tailwind and back, and HTML to JSX. Utilities include a JWT decoder, Base64 and URL encoders and decoders, a Unix timestamp converter, a regex tester and HTML entity tools.

Learning resources

The site also publishes cheatsheets for TypeScript, Zod and Tailwind, guides to TypeScript types, generics, utility types, strict mode and using TypeScript with React, and comparisons such as TypeScript versus JavaScript and Zod versus Yup, Joi and Valibot.

Who it suits

JS2TS suits developers migrating small JavaScript files or snippets to TypeScript, learners who want to see how plain JavaScript maps to typed code, and anyone who needs a quick conversion between data formats.

Things to consider

AI-inferred types are a starting point. The converter cannot always know the real shape of your data, so it may produce types that are too loose, such as any, or too narrow. Review the output, run the TypeScript compiler in strict mode and add tests before committing. For a large codebase, migrating file by file within your own tooling is usually safer than pasting code into a website. Avoid pasting proprietary code or secrets such as API keys, and decode JWTs containing sensitive data only if you trust where they are processed. The site carries sponsor placements.