Tips for accurately defining the return type for querySelector(All) connections

I enjoy doing this particular task, ensuring the types are correct.

const qs = document.querySelector.bind(document) as HTMLElementTagNameMap | null;
const qsa = document.querySelectorAll.bind(document) as NodeListOf<any>;

While hovering over querySelectorAll in my code editor, I see a lot of information like "return Type of 

NodeListOf<...> (+2 overloads)
", but I am unsure of what those overloads mean and how to use <...>. Therefore, I tried ...

However, I encounter errors with qsa stating that 

NodeListOf<any> has no callable signatures
.

typescriptbinddeclare

Answer №1

You can let TypeScript infer the type without having to explicitly declare it:

const qs = document.querySelector.bind(document);
const qsa = document.querySelectorAll.bind(document);

Playground link

The issue with your approach was specifying the type of result instead of the type of the function.

If you ever need to explicitly define a function's type in TypeScript, use typeof in a type context like this:

type QSFunction = typeof document.querySelector;

or

const qs = document.querySelector.bind(document) as typeof document.querySelector;

Playground link

When using typeof in an assignment or casting context, it refers to TypeScript's type system, not JavaScript's. Just remember, it's not necessary in this scenario.

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