unknown vs any in TypeScript: What to Choose in 2025?

Introduction: Why Did This Topic Blow Up on Stack Overflow?

\n

If you've ever written in TypeScript, you've likely faced the dilemma: unknown or any? The question, which has gathered thousands of views on Stack Overflow, remains relevant in 2025. It seems both types allow you to store anything — so what's the difference?

\n\n

Imagine you're building a house. any is a door wide open to everyone, including burglars. unknown is a door with a lock and a peephole: you check who's there first, and only then let them in. In this article, we'll figure out why unknown has become the gold standard for safety in TypeScript, and any is the evil that is sometimes justified.

\n\n

We won't just rehash the documentation. We'll show real-world cases from 2025 practice, break down best practices, and give a clear decision-making algorithm. Let's go!

\n\n

What is any and Why is Everyone Afraid of It?

\n\n

any is the most "flexible" type in TypeScript. It literally tells the compiler: "Turn off the type system, I know what I'm doing." It sounds like a superpower, but in reality, it's a ticking time bomb.

\n\n

Example: How any Breaks Types

\n

function processUser(user: any) {\n    console.log(user.name.toUpperCase()); // Runtime error if user is null\n}\n\nprocessUser(null); // TypeError: Cannot read property 'toUpperCase' of null

\n\n

The TypeScript compiler won't even warn you about this! any disables all checks, and the error will only surface in production. In 2025, when projects are becoming more complex, this approach is a path to chaos.

\n\n

When is any Still Useful?

\n

\n
• Migration from JavaScript: when rewriting an old project, any is a temporary crutch.
\n
• Dynamic data: for example, responses from external APIs where the structure changes.
\n
• Tests: in mocks, it's sometimes easier to use any than to describe complex types.
\n

\n\n

But remember: any is like a credit card with an unlimited limit. Convenient, until the bill arrives.

\n\n

Unknown: The Strict Guard at the Entrance

\n\n

unknown appeared in TypeScript 3.0 as a safe alternative to any. It can also contain any value, but forbids working with it without explicit checking. It's a container type that requires verification.

\n\n

Example: unknown in Action

\n

function processUser(user: unknown) {\n    // Compilation error! Property 'name' does not exist on type 'unknown'\n    // console.log(user.name.toUpperCase()); \n    \n    // Need a check\n    if (user && typeof user === 'object' && 'name' in user) {\n        const typedUser = user as { name: string };\n        console.log(typedUser.name.toUpperCase()); // All good\n    }\n}\n\nprocessUser({ name: "Alice" }); // ALICE\nprocessUser(null); // Nothing will crash

\n\n

Notice the difference? unknown doesn't let you shoot yourself in the foot. You must check the type before using it. This is safe typing.

\n\n

Comparison of any vs unknown in a Table

\n\n

To solidify the material, let's look at the key differences:

\n\n\n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n

Criterion	any	unknown
Assigning any value	✅ Yes	✅ Yes
Accessing properties without checking	✅ Yes	❌ No
Assigning to another type	✅ Any	❌ Only any or unknown
Protection from runtime errors	❌ No	✅ Yes (requires checking)

\n\n

As you can see, unknown wins