Differences Between any and unknown in TypeScript

In TypeScript there are two types that can be used to represent any values: any and unknown. Although both types allow working with any values, their behavior and safety in the context of types differ.

any Type

The any type is used when you want to indicate that a value can be of any type. This allows working with variables whose types aren't known at compile time, but at the same time any removes type restrictions, allowing you to do anything with the variable.

Advantages of using any

• Flexibility: allows working with variables whose type is unknown in advance or variable.
• Convenience: convenient when integrating with external libraries when types aren't defined, or when you need to temporarily disable type checking.

Disadvantages of using any

• Loss of type safety: using any weakens TypeScript's type system, allowing errors that won't be caught at compile time.
• Complicates code maintenance: due to lack of type information, it can become difficult to understand what values can be assigned to a variable.

any usage example

let value: any;

value = 42; // Number
value = "Hello"; // String
value = { name: "John" }; // Object

value.someMethod(); // Error won't be detected at compile time

unknown Type

The unknown type is a safer alternative to any. With unknown you can still work with a variable of any type, but you need to check its type before performing operations on it. That is, unlike any, you won't be able to perform operations with an unknown type variable without checking its type.

Advantages of using unknown

• Type safety: although unknown allows working with any types, TypeScript compiler requires you to perform a type check before performing any operations with the value. This helps avoid errors and maintains type safety.
• Is a safer choice: unknown preserves TypeScript's type system, requiring explicit checking before using a value.

Disadvantages of using unknown:

• Not as flexible as any: before using an unknown type variable, you need to perform a type check, which adds extra code.

unknown usage example

let value: unknown;

value = 42; // Number
value = "Hello"; // String

// Compilation error: can't call methods on `unknown` type
value.someMethod(); 

// Need to perform type check before using
if (typeof value === "string") {
  console.log(value.toUpperCase()); // Now it's safe
}

When to use any vs unknown?

• Use any when you know for sure that you don't need to check the type, or in cases where the type can't be precisely determined, for example, when working with dynamic data or third-party libraries without types.
• Use unknown when you need to work with variables whose type is unknown, but you want to maintain type safety by performing explicit type checking before using data.