JavaScript developers adopting TypeScript

JavaScript to TypeScript: Side-by-Side Syntax

A migration reference for JavaScript developers adopting TypeScript. Each topic shows the JavaScript you already know on the left and the TypeScript equivalent on the right, highlighting what changes and what stays the same.

Topics

Side-by-side syntax breakdowns organized by concept.

JavaScript to TypeScript Variables

What changes (and what stays identical) when you add TypeScript annotations to JavaScript variables.

JavaScript to TypeScript Functions

What changes when you add TypeScript types to JavaScript functions -- parameter annotations, return types, optional arguments, and overloads.

JavaScript to TypeScript Types

How TypeScript's type system formalizes patterns that JavaScript developers already use informally through duck typing and typeof checks.

JavaScript to TypeScript Interfaces

How TypeScript interfaces formalize the implicit object contracts that JavaScript developers maintain through convention and documentation.

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