Usecases and Errors in TypeScript

type for filterIds

In the code below, the filter_ids value is extracted from the query parameters of the incoming request req. It first checks if req.query.filter_ids exists and is of type string, then it splits the string into an array using the split method, maps each element to a number using map, and casts the result as an array of FilterIds.

const filterIds: FilterIds =
      (req.query?.filter_ids as string | undefined)?.split(",")?.map((id: string) => +id) as FilterIds;

This code can be re-written in a more concise manner:

const filterIds: FilterIds =
      (req.query?.filter_ids as string)?.split(",").map(Number) || [];

Best practices for nullish coalescing and optional chaining in Typescript

The original code snippet is using optional chaining and the ternary operator to extract the first match from a regular expression on an optional string, and assign it to a variable that can either be a string or null. In typescript, it's recommended to use nullish coalescing and the optional chaining operator together for more concise and readable code.

let updatedAddress2 = address2?.match(/\d+/g);                  // might be an array or undefined
updatedAddress2 = updatedAddress2 ? updatedAddress2[0] : null;  // might be null or string

Recommended code:

const updatedAddress2: string | null = address2?.match(/\d+/g)?.[0] ?? null;

useEffect can only return Promise and undefined

useEffect(() => {
    if (status === "unauthenticated")
      // ❌ return router.replace("/");
      router.replace("/");
  }, [status]);

Expected 0 type arguments but got 1

This error usually occurs when you try to pass a type argument to a function that doesn't accept any type arguments.

For example, if you have a function that is defined as follows:

function myFunction() {
  // function body
}

You cannot pass any type arguments to this function because it doesn't accept any.

So, if you try to call this function like this:

myFunction<string>(); // Error: Expected 0 type arguments, but got 1.

You will get the error Expected 0 type arguments, but got 1. because you're trying to pass a type argument to a function that doesn't accept any.

To fix this error, you need to either remove the type argument, or modify the function definition to accept the type argument.