JavaScript Input
TypeScript Output
Convert JavaScript code to TypeScript with type annotations
Convert JavaScript code to TypeScript automatically. This tool adds type annotations, converts var to let/const, adds interfaces for objects, and applies TypeScript best practices to your JavaScript code.
1. Start with .ts Extension
Rename .js files to .ts and fix errors gradually
2. Enable Strict Mode
Use "strict": true in tsconfig.json for better type safety
3. Add Types Incrementally
Start with any types, then refine to specific types
4. Use Type Definitions
Install @types packages for third-party libraries
// JavaScript
var name = "John";
// TypeScript
const name: string = "John";// JavaScript
function add(a, b) {
return a + b;
}
// TypeScript
function add(a: number, b: number): number {
return a + b;
}// JavaScript
const user = {
name: "John",
age: 30
};
// TypeScript
interface User {
name: string;
age: number;
}
const user: User = {
name: "John",
age: 30
};Q: Will my JavaScript code break in TypeScript?
A: No, all valid JavaScript is valid TypeScript. You can gradually add types without breaking existing code.
Q: Do I need to convert everything at once?
A: No, you can migrate file by file. TypeScript supports mixed JS/TS projects.
Q: Is this tool free?
A: Yes, completely free with no signup required. All processing happens in your browser.