Learn TypeScript Easily: Two Powerful Features

TypeScript adds types to JavaScript, helping developers catch bugs early. In this blog, we’ll look at two helpful concepts in TypeScript: the differences between any, unknown, and never, and how the keyof keyword works.

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1. Difference Between any, unknown, and never in TypeScript

These three special types help define how data should behave in your code.

any

• It disables type checking.
• Anything can be assigned to it, and it can be assigned to anything.
• It's useful when you're migrating JS code but should be avoided in large projects.

let value: any = "Hello";
value = 42; // No error
value.toUpperCase(); // No error, but can crash at runtime if value is not a string

unknown

• Like any, but safer.
• You must check the type before using it.

let input: unknown = "World";
if (typeof input === "string") {
  console.log(input.toUpperCase());
}

never

• Used when a function never returns.

• For example, functions that throw errors.

function throwError(msg: string): never {
  throw new Error(msg);
}

2. What is the use of the keyof keyword in TypeScript?

• The keyof keyword is used to create a union of string literal types from the keys of an object or interface. This is powerful for creating generic and reusable code.

type User = {
  name: string;
  age: number;
  email: string;
};

type UserKeys = keyof User; // "name" | "age" | "email"

function getValue<T, K extends keyof T>(obj: T, key: K): T[K] {
  return obj[key];
}

const user: User = {
  name: "Kawsar",
  age: 22,
  email: "kawsar@example.com"
};

const userName = getValue(user, "name"); // returns "Kawsar"

Conclusion

Understanding special types like any, unknown, and never helps you write safer code. The keyof keyword makes your code more flexible and reusable.

Thanks for reading!

Happy coding and keep exploring TypeScript!.

Useful Links:

• Assignment 1 documentation

• task one