Free Online Tool

JavaScript to TypeScript Converter

Paste your JavaScript and get TypeScript with inferred types, interface extraction, JSDoc-to-type migration, and strict-mode fixes — instantly in your browser.

strict mode infer return types extract interfaces convert JSDoc convert const enums Target: Module:

JavaScript Input

0 lines · 0 chars

TypeScript Output

Ready

INFOLoad an example or paste JavaScript and click Convert.

JavaScript to TypeScript Converter

This tool converts JavaScript (.js) to TypeScript (.ts) by applying a comprehensive set of transformations: adding type annotations to function parameters and return types, extracting object shapes as interface declarations, converting JSDoc @param and @returns tags to TypeScript types, and enabling strict-mode compatible patterns.

What Gets Converted

Function parameters annotated with inferred or any types
Arrow functions get typed signatures
Object literals extracted as interface definitions
JSDoc @param {type} name → TypeScript parameter types
var → let / const (based on reassignment)
Const object maps converted to const enum
Class properties annotated with inferred types
CommonJS require() → ES module import
module.exports → export statements

Limitations

This is a source-text converter, not a full TypeScript compiler. Complex runtime type narrowing, dynamic property access, and highly generic code may still require manual type annotation after conversion. For large codebases, consider using the official TypeScript compiler's allowJs flag as a starting point.