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Karishma Shukla
Karishma Shukla

Posted on • Updated on

'any' vs 'unknown' in TypeScript

When you start learning TypeScript, you will come across two types - "any" and "unknown"

any - The any type allows us to assign literally β€œany” particular value to that variable, simulating what we know as plain JavaScript.

unknown - The unknown type is the type-safe counterpart of any. Anything is assignable to unknown, but unknown isn't assignable to anything but itself and any without a type assertion or a control flow based narrowing.

Let's understand with an example.

let age: number;
let userAge: any;

userAge = 'This is some age';
userAge = 20;

age = userAge;
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This code works! πŸŽ‰
Type of userAge is any so it can be assigned any value - string, number etc.

let age: number;
let userAge: unknown;

userAge = 'This is some age';
userAge = 20;

age = userAge;
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The statement age=userAge gives an error.
The type is unknown so what is the problem here?
To assign an unknown value to a value with a fixed type, we have to do some quick type check!

let age: number;
let userAge: unknown;

userAge = 'This is some age';
userAge = 20;

if(typeof userAge === 'number') {
  age = userAge;
}
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And now this works too! πŸŽ‰

When to use what?

You shouldn't use either of them. But if you really have to then unknown is a better choice if you know what you want to do with that value eventually.
I don't recommend using any - it takes away the actual essence of TypeScript!

Top comments (3)

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johnkey profile image
INDERA SHAH

πŸ‘πŸ‘πŸ‘πŸ‘

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jesusparra profile image
JesusParra

Thanks, it was easy to understand!

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patrickcodes profile image
Patrick

This is great πŸ‘πŸ‘
Most of the blogs are too long to read. This explains it very quickly.
Thank you!