What is the difference between between type any and unknown?

The `any` and `unknown` types in TypeScript both serve as top types, meaning they can represent any possible JavaScript value. However, they differ in how they enforce type checking and safety.

1. **any Type:**

   • The `any` type essentially opts out of type checking. When you use any, you're telling TypeScript that the variable can be anything, and thus TypeScript won't enforce any checking on the operations you perform on it.

   • It's like a way to tell TypeScript to trust you on what you're doing, as you're bypassing the compiler's checks.

   • Using `any` can lead to a loss of the benefits of TypeScript, as it can propagate through your code and make it more like plain JavaScript in terms of type safety.

2. **unknown Type:**

   • The `unknown` type was introduced in TypeScript 3.0 as a type-safe counterpart to any.

   • A variable of type `unknown` represents a value that could be anything, but unlike `any, you cannot perform arbitrary operations on a value of type unknown` without first asserting or narrowing its type to a more specific type.

   • This means that while you can assign any value to a variable of type unknown, you can't do much with it without some form of type checking (like using type assertion or type narrowing).

Example to Illustrate the Difference:

let valueAny: any;

let valueUnknown: unknown;

valueAny = 123; // OK

valueUnknown = 123; // OK

let value1: string = valueAny; // OK: No error, but potentially unsafe

// let value2: string = valueUnknown; // Error: Type 'unknown' is not assignable to type 'string'

valueAny.method(); // OK: TypeScript doesn't check.

// valueUnknown.method(); // Error: Object is of type 'unknown'.

if (typeof valueUnknown === 'string') {

  let value3: string = valueUnknown; // OK: type is narrowed to 'string'

}

In summary, `unknown` is a safer alternative to `any. While any` allows you to perform any operations on the variable, potentially leading to runtime errors, `unknown` requires you to explicitly check or assert the type of the variable before performing operations on it, thereby increasing the type safety of your code.