How This JavaScript to TypeScript Converter Works
Paste JavaScript and this js to ts converter online produces TypeScript-flavored output instantly, no upload, no signup, no server round trip. It's a genuine convert javascript to typescript workflow, parameter types, module syntax, and var declarations are all rewritten as you type.
Parameter Types and the unknown Placeholder
This typescript param types generator adds : unknown to any function parameter, named function or arrow function, that doesn't already have a type annotation, unknown is TypeScript's safest placeholder since it forces you to narrow the type before using the value, unlike any which silently disables type checking. This add types to javascript pass is intentionally conservative, it won't guess string or number from how a parameter is used, that requires real type inference this regex-based tool doesn't attempt. A var to let converter pass also runs automatically, replacing every var declaration with let, matching modern TypeScript style guides that discourage var entirely.
Module Syntax: require() to import, module.exports to export default
As a require to import converter it rewrites both plain and destructured require() calls, const foo = require('bar') becomes import foo from 'bar', and const { a, b } = require('bar') becomes import { a, b } from 'bar'. A module.exports to export default pass handles the single most common CommonJS export pattern, module.exports = someValue becomes export default someValue, though named exports written as module.exports.foo = ... aren't rewritten and need a manual pass.
Limitations and What to Review Manually
This javascript to typescript converter free tool is a genuine js to ts migration tool for a first-pass conversion, quick prototyping, or learning how CommonJS maps to ES module syntax, not a full compiler-grade transform. It's regex-based, not an AST parser, so review the output rather than trusting it blindly, in particular the automatic return-type annotation is unreliable, it can add a return type that doesn't match what the function actually returns, always double-check return types by hand rather than assuming they're correct.