What Is TypeScript?

TypeScript compiles to plain JavaScript. Every valid JavaScript file is a valid TypeScript file. You opt into more safety by adding type annotations — and the TypeScript compiler tells you when you're calling a function with the wrong arguments, accessing a property that doesn't exist, or returning the wrong shape from an API.

The core value proposition:

// Without types — silent bugs
const price = getPlan().price; // might be undefined
const total = price * quantity; // NaN in production

// With types — caught at compile time
const plan: Plan = getPlan(); // Plan.price is always number
const total: number = plan.price * quantity; // guaranteed correct

Why TypeScript matters for SaaS teams:

• Refactoring is safe — the compiler tells you every callsite that breaks
• API contracts are enforced — mismatched request/response shapes fail at build time, not runtime
• Autocomplete is accurate — the IDE knows exactly what properties are available
• Onboarding is faster — new developers understand data shapes from the types, not from running the code

TypeScript in a Next.js + Supabase stack: Supabase CLI generates TypeScript types from your database schema. Every table, every column, every function — typed automatically. Combined with Next.js's typed API routes, you get end-to-end type safety from the database query to the React prop.

Should your MVP use TypeScript? Yes. The setup overhead is minimal. The bugs it prevents in the first month of production pay it back immediately.