Before we dig into the any and unknown types, let’s review what TypeScript is. TypeScript is a statically typed superset of JavaScript, developed and maintained by Microsoft. It aims to address JavaScript’s limitations by providing optional static types, enhancing IDE features, and promoting safer, more robust code.

The any Type

In TypeScript, the any type is the most capable type. Anything can be assigned to an any type, and any can be assigned to anything. It is, quite literally, a wildcard.

let wildcard: any = "I am a string";
wildcard = 42; // it's okay
wildcard = []; // it's still okay
wildcard.foo.bar.baz; // it's incredibly okay!

In a sense, any provides an escape hatch from TypeScript’s type system. When you define a variable as, you’re essentially telling TypeScript to trust your judgment and let you manage this variable without the usual safety checks.

While this might sound great on the surface, overuse of any is generally discouraged because it bypasses TypeScript’s type-checking and reduces the benefits of the language. If you’re using any all over your codebase, you’re not really using TypeScript; you’re essentially using verbose JavaScript.

The unknown Type

TypeScript 3.0 introduced the unknown type as a type-safe counterpart of any. The unknown type represents any value just like, but TypeScript enforces checks before any operation is carried out on an unknown value, or before it’s assigned to a variable of a different type.

let mystery: unknown = "I am a string";
mystery = 42; // it's okay
mystery = []; // it's still okay
mystery.foo.bar.baz; // TypeScript Error! Object is of type 'unknown'.

Here, TypeScript is enforcing type checks on the mystery variable, and any operation without a type guard results in a compile-time error. unknown allows us to have a strict type-checking system, where we cannot make assumptions about the type.

any vs unknown

So, what’s the fundamental difference between any and unknown?

The any type is TypeScript’s most lenient type, allowing developers to opt-out of type-checking for specific variables. It offers maximum flexibility at the cost of safety, and the compiler trusts that the programmer knows what they’re doing.

On the other hand, unknown is the type-safe counterpart of any. While it also represents any type of value, TypeScript doesn’t allow you to conduct operations on unknown variables or assign them to other types without some kind of type assertion or type guarding. unknown encourages developers to handle types explicitly and make fewer assumptions about the data.

Conclusion

In essence, any and unknown provide flexibility for working with dynamic or complex data structures in TypeScript. While any providing complete freedom with reduced safety, unknown and ensuring robust type safety, fostering a stricter and more reliable coding environment.

It’s important to understand these distinctions and their implications on your code’s safety and maintainability. The choice between any and unknown should depend on the specific needs of your code, balancing the flexibility and safety provided by TypeScript’s unique type system.