Is it a Typescript error or is Typescript's checking not entirely accurate?

After years of experience with JavaScript, I recently decided to delve into TypeScript.


Example 1

As I was developing, I discovered that

const A : B = class B {}

This code snippet would result in a warning "Cannot find name 'B'".

However, the following will not.

class B {}

const A : B = B ;

Example 2

Another example is

class B {}

const A : B = B ;

const C : A = A ;

This will trigger a warning "Cannot find name 'A'"


It seems that tsc checking only recognizes anything starting with "class".

In JavaScript, there doesn't appear to be any issues. Compiling them all even works....

So my concern is, it might just be that the tsc checking isn't thorough enough..., however, if I circumvent this, I'll lose the purpose of type checking, so I may have to adjust my writing style.

Can you offer advice on whether I'm mistaken? Or is there another reason for the error?

Answer №1

In order to use a class as a type, it must be defined first.

Additionally, in your third scenario, you are trying to designate a constant as a type which is not possible because A has not been given a class definition. It's recommended to refer to Typescript's documentation on class and type definitions for a more comprehensive explanation.

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