TypeScript vs JavaScript in Boilerplates

TL;DR

In 2026, the question isn't whether to use TypeScript — it's how strictly. 98%+ of SaaS boilerplates ship TypeScript by default. The benefits are real: fewer runtime bugs, better DX, and type-safe API layers. The downside: TypeScript adds setup friction and any-heavy code is worse than JavaScript.

The Current State

A sample of popular boilerplates:

Boilerplate	Language	TypeScript Strictness
T3 Stack	TypeScript	Strict (strict: true)
ShipFast	TypeScript	Moderate
Supastarter	TypeScript	Strict
Makerkit	TypeScript	Strict
Epic Stack	TypeScript	Strict
Open SaaS	TypeScript	Moderate

JavaScript-only boilerplates in 2026: nearly zero in the mainstream.

Why TypeScript Won

1. Type-Safe API Layers (tRPC Changed Everything)

tRPC gives you end-to-end type safety between server and client — but only with TypeScript:

// Server: define your API once
const postRouter = createTRPCRouter({
  getById: publicProcedure
    .input(z.object({ id: z.string() }))
    .query(async ({ input }) => {
      return prisma.post.findUnique({ where: { id: input.id } });
    }),
});

// Client: full type inference — no manual types
const { data: post } = api.post.getById.useQuery({ id: '123' });
//      ^^^^ TypeScript knows: post is Post | null
//           post.title, post.content, etc. are all typed

Without TypeScript, you lose the entire benefit of tRPC. This alone drove TypeScript adoption in the boilerplate ecosystem.

2. Database Schema → Type Safety

Prisma generates TypeScript types from your database schema:

// prisma/schema.prisma
model User {
  id        String   @id @default(cuid())
  email     String   @unique
  name      String?
  plan      Plan     @default(FREE)
}

enum Plan {
  FREE
  PRO
  ENTERPRISE
}

// Prisma generates:
// - User type
// - CreateUserInput type
// - Plan enum

// TypeScript knows User.plan is Plan.FREE | Plan.PRO | Plan.ENTERPRISE
// Missing a case in a switch statement is a compile error, not a runtime bug
const getFeatures = (plan: Plan) => {
  switch (plan) {
    case Plan.FREE: return ['Basic'];
    case Plan.PRO: return ['Basic', 'Advanced'];
    case Plan.ENTERPRISE: return ['Basic', 'Advanced', 'Enterprise'];
    // TypeScript enforces exhaustive checks
  }
};

3. Catch Bugs at Build Time

The classic JavaScript pain point:

// JavaScript — this crashes at runtime
const user = await getUser(userId);
console.log(user.emal);  // Typo: should be 'email' — you find out at runtime

// TypeScript — caught at compile time before deployment
const user = await getUser(userId);
console.log(user.emal);
//               ^^^^ Error: Property 'emal' does not exist on type 'User'
//               Did you mean 'email'?

For SaaS with paying customers, "find out at runtime" means "find out when a customer reports a bug."

4. Refactoring Confidence

Large codebases live and die by refactoring. TypeScript makes it safe:

// Rename a field in Prisma schema: subscriptionStatus → billingStatus
// TypeScript immediately shows every reference that needs updating
// 47 errors across 12 files — all addressable before deployment

Without TypeScript, renaming is dangerous manual work.

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Where TypeScript Falls Short

The any Escape Hatch is a Footgun

Poorly written TypeScript is worse than JavaScript:

// This is technically TypeScript but provides zero safety
const processPayment = (data: any) => {
  // data could be anything — no protection
  stripe.charges.create({ amount: data.amnt });  // Typo: amnt vs amount
  // TypeScript won't catch this because data is `any`
};

Boilerplates with any scattered throughout are red flags during evaluation.

TypeScript Slows Initial Development

Setting up types for third-party libraries, handling null | undefined, and fighting the compiler when prototyping can slow you down early. For 48-hour hackathons, TypeScript overhead is real.

Complex Types Become Unreadable

Over-engineered TypeScript is a real problem:

// When TypeScript gets out of hand
type DeepPartial<T> = T extends object ? {
  [P in keyof T]?: DeepPartial<T[P]>;
} : T;

type PickByValue<T, V> = {
  [K in keyof T as T[K] extends V ? K : never]: T[K];
};

Great for library authors. Terrible for product code.

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Practical TypeScript in Boilerplates

The best boilerplates use TypeScript pragmatically:

// Good: strict types for domain logic
interface CreateUserInput {
  email: string;
  name: string;
  plan: 'free' | 'pro' | 'enterprise';
}

async function createUser(input: CreateUserInput): Promise<User> {
  return prisma.user.create({ data: input });
}

// Acceptable: assertion when you know better than TypeScript
const stripeEvent = stripe.webhooks.constructEvent(
  body, signature, secret
) as Stripe.DiscountCreatedEvent;  // You've already checked event.type

// Anti-pattern: avoid casting to escape type errors
const user = await getUser() as any;  // Never do this

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JavaScript Still Makes Sense When

• Prototyping an idea before committing to a stack
• Team is exclusively JavaScript-background with tight timeline
• Scripts, migrations, one-off tooling (not production app code)
• Simple Next.js marketing sites with no complex business logic

For anything with paying users, TypeScript's benefits outweigh the overhead by a wide margin.

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What to Look for in a Boilerplate

Good TypeScript signals:

• "strict": true in tsconfig.json
• No @ts-ignore comments
• Zod for runtime validation (TypeScript doesn't validate at runtime)
• Generated types from Prisma/database schema

Bad TypeScript signals:

• Widespread any types
• tsconfig.json with "strict": false
• Type assertions (as X) to silence compiler errors
• No runtime validation (TypeScript types don't protect at API boundaries)

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Find TypeScript-first boilerplates on StarterPick.