CODEWITHSUNDEEP
typescript
Valentin Parsy
Valentin Parsy

Reputation: 395

Why is it impossible to use a var in a type definition ?

type myType = 'A';
const myVar = 'A';

let a: 'A'; // OK
let b: myType; // OK
let c: myVar; // ERROR : cannot find name 'myVar'

Why isn't it possible to use a var as a type ? Shouldn't it be possible ?

Upvotes: 0

Views: 78

Answers (2)

Ankush Jain
Ankush Jain

Reputation: 7059

There are 4 ways to delcare a variable in TypeScript

var, let, const & Type (Type will be custom datatype)

let & var are quite similar while const prevent re-assignment to a variable. You can find diff between var & let here.

const is something which is constant and it's behaviour in TypeScript is same as C#. In C#, we also can't use const as type.

And to mainly answer your question - myVar is a variable not a type so you can't use a variable as type.

Upvotes: 2

Titian Cernicova-Dragomir
Titian Cernicova-Dragomir

Reputation: 249666

myVar is a constant, you cannot type a variable as a constant, you can specify that a variable has the same type as the constant:

let c: typeof myVar;

Note that since the constant is "A" the above declaration is the same as 

let c: "A";

So the only value assignable tp c is the constant value "A"

Upvotes: 2

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