RTK: selectors and type inferring

[dakur]

Hi again, I need please some more help with typings in RTK, this time when defining selectors. This simple selector which takes advantage of createSelector() should work in my opinion:

import {createSelector} from '@reduxjs/toolkit';

function pages(state: State): Page[]
{
  return state.material.pages;
}

function commentsFromAllPages(): Comment[][]
{
  const out = createSelector(
    [pages],
    (pages) => {
      const comments = pages.map((page) => page.comments);
      return comments;
    },
  );
  return out;
}

But it's giving me strange typing error (notice also the type at the line with const out):

I've checked for generic arguments or something, but did not find anything.. Can you point me in some direction, please?

Thanks in advance.

[EskiMojo14]

createSelector returns an instance of a selector. you should use it like this:

import { createSelector } from '@reduxjs/toolkit';

function selectPages(state: State): Page[] {
  return state.material.pages;
}

const selectCommentsFromAllPages = createSelector(
  [selectPages],
  (pages) => {
    const comments = pages.map((page) => page.comments);
    return comments;
  },
);

[dakur]

🤦‍♂️ Oh yes, now I see it, thanks!

[dakur]

not really true, see below

---

Just to clarify – it's enough to remove the return type from the selector:

---function commentsFromAllPages(): Comment[][]
+++function commentsFromAllPages()
{
  const out = createSelector(
    [pages],
    (pages) => {
      const comments = pages.map((page) => page.comments);
      return comments;
    },
  );
  return out;
}

It will be then inferred correctly:

[dakur]

Sorry, it's not, now I understand it's a "replacement" for the function. 🙂