Why I Swear By Strict Typing in Large React Projects (and Why You Should Too)

If you’ve ever worked on a mid-to-large React codebase, you’ve probably experienced the pain of mysterious bugs, confusing props, or teammates accidentally breaking components without warning. TypeScript’s strict mode isn’t just a checkbox — it’s a powerful tool that can transform your developer experience and project architecture by catching subtle errors early, improving collaboration, and giving you more confidence in your code.

Today, I want to share why strict typing is my go-to in large React projects, how it saves me time and headaches, and practical tips to adopt it incrementally without burnout.

What Does Strict Typing Mean in React Projects?

Strict typing means enabling TypeScript’s strictest compiler settings, such as:

• strictNullChecks: Prevents null or undefined sneakily creeping into values.
• noImplicitAny: Forces you to declare types explicitly instead of falling back to any.
• strictFunctionTypes: Makes function type assignments safer.
• strictBindCallApply: Tightens safety on methods like .bind, .call, and .apply.
• alwaysStrict: Ensures files are parsed in strict mode.

Once these flags are on (usually in your tsconfig.json), your code stops guessing about types — and starts enforcing them rigorously.

In React specifically, strong typings guard your components’ props and state, catching:

• Wrong or missing props.
• Unexpected null or undefined values at runtime.
• Incorrect function signatures passed as callbacks.

Strict typing pushes you to design more predictable API surfaces between components, which is golden as your app grows.

Common Bugs Caught Early Thanks to Strict Types

There are bugs I used to spend hours hunting that strict types now stop cold at compile-time.

Example: Hidden null references in props

For example, consider this component:

type User = {
  id: number;
  name: string;
  email?: string | null;
};

type Props = {
  user: User;
};

export function UserProfile({ user }: Props) {
  // Without strictNullChecks, user.email could be null and cause runtime crash:
  return <p>Contact: {user.email.toLowerCase()}</p>;
}

If strictNullChecks is disabled, TypeScript lets user.email be null or undefined, and you’d only find your bug when calling .toLowerCase() on null at runtime.

With strictNullChecks, this instantly errors:

Object is possibly 'null'.

Now you handle the case explicitly:

<p>Contact: {user.email ? user.email.toLowerCase() : "N/A"}</p>

Example: Prop union types prevent invalid inputs

When components accept varied but specific props, union and intersection types let you encode that precisely:

type SuccessProps = {
  status: "success";
  data: string;
};

type ErrorProps = {
  status: "error";
  error: Error;
};

type LoadingProps = {
  status: "loading";
};

type Props = SuccessProps | ErrorProps | LoadingProps;

export function StatusMessage(props: Props) {
  switch (props.status) {
    case "success":
      return <p>Data: {props.data}</p>;
    case "error":
      return <p>Error: {props.error.message}</p>;
    case "loading":
      return <p>Loading...</p>;
  }
}

This pattern guarantees you can only provide relevant props for each state. No more risking error prop when status is "success".

Your editor’s autocomplete will also guide you perfectly here — another huge DX win.

How Strict Typing Improves Developer DX

Strict typing might feel like a burden upfront, but it directly enhances developer experience in several ways:

• Fast feedback loop: Errors appear instantly in your editor and compile step — no need for manual test or runtime guesswork.
• Better autocomplete: Editors fill in accurate props and method signatures, reducing mental overhead and lookup time.
• Safer refactors: Rename or change a prop and the compiler shows all callsites that must change with zero runtime surprises.
• Team alignment: Everyone shares a strict, formal contract for component APIs, making onboarding and collaboration smoother.

For me, this means spending way less time in debugger or explaining bugs with teammates — and more time shipping features.

Real-World Examples from My Projects

In a recent React+TypeScript project with a 6-person team, here’s how strict typing saved big:

• Catch typos in API payload shapes: Our backend data often changed shape, but strict types caught mismatches right when fetching — preventing UI crashes.
• Guard against undefined props: A component expected a callback prop but sometimes received undefined. With strictNullChecks, compilation failed, forcing explicit defaults or handlers.
• Safer UI state machines: We typed complex union states throughout reducers, stopping accidental state transitions at compile time.

One tricky debugging session to highlight: A chat app had a rare race condition where a message arrived slightly incomplete. Types flagged the partial state shape mismatch immediately, saving us hours of painful log spelunking.

Tips to Adopt Strictness Incrementally

If you’re intimidated by strict mode turning your whole codebase red overnight, ease in gradually:

1. Enable strictNullChecks first: This often yields most of the runtime safety benefits.
2. Fix errors step-by-step: Tackle one directory or component at a time.
3. Use // @ts-expect-error sparingly: Instead of turning off strict settings globally, annotate and fix ignored errors explicitly.
4. Add JSDoc and return types: Annotate tricky functions to guide TypeScript without guessing.
5. Pair with ESLint rules: Auto-fix some issues and maintain consistency.
6. Leverage IDE tooling: Most modern editors will autofill and highlight strictness gains, making fixes more pleasant.

Quick Checklist: Enabling Strict Typing in Your Project

{
  "compilerOptions": {
    "strict": true,                // Enables all strict flags
    "noImplicitAny": true,
    "strictNullChecks": true,
    "strictFunctionTypes": true,
    "strictBindCallApply": true,
    "noImplicitReturns": true,
    "noFallthroughCasesInSwitch": true,
    "alwaysStrict": true,
    "jsx": "react-jsx"
  }
}

Remember, you don’t have to flip all switches at once, but this is the gold standard for React apps with TypeScript.

In Summary

Strict typing in React projects pays off most when your codebase grows and you work with others — the upfront work is rewarded with:

• Early, explicit bug detection
• Easy-to-use, autocomplete-rich APIs
• Safer refactors and better maintainable code
• Improved team trust and onboarding speed

It’s not about perfection or never touching any — it’s about using types as living documentation that guide your development and save hours of debugging later.

Start small, be patient, and watch the benefits grow.

Until next time, happy coding 👨‍💻
– Patricio Marroquin 💜