What steps can be taken to troubleshoot the "error is not assignable to parameter of type" issue in

Question

What steps can be taken to troubleshoot the "error is not assignable to parameter of type" issue in

Do you have any suggestions on how to specify to TypeScript that I am passing the same required argument? Currently, I am encountering an error stating (is not assignable to parameter of type '{ [key: string]: ""; } ). If you could provide guidance on how to declare types in this scenario, it would be greatly appreciated.

  const initialState = { name: '', gender: '', height: '', weight: '' };
  const [selected, setSelected] = useState<{ [key: string]: '' }>(initialState);

I attempted a solution, but it appears to involve redundant code

  type state = { [key: string]: '' };
  const initialState: state = { name: '', gender: '', measurements: '', height: '', weight: '' };
  const [selected, setSelected] = useState<state>(initialState);

typescript

Answer 1

Answer №1

Here is a more effective way to express the same concept:

const initialState = { name: '', gender: '', height: '', weight: '' };
const [selected, setSelected] = useState<typeof initialState>(initialState);

The issue with your method lies in how TypeScript interprets the type and how you envision it to be.

You seem to believe that the inferred type looks like this:

{ [key: string]: '' }

This indicates that any key can be used but only with an empty string value i.e. ''.

However, TypeScript typically infers it differently (which aligns more with common practice) as shown below:

{
    name: string;
    gender: string;
    height: string;
    weight: string;
}

Therefore, when you declare,

const [selected, setSelected] = useState<{ [key: string]: '' }>(initialState);

You are assigning a broader type to a narrower one. TypeScript assumes that the values in initialState can have a string type while you are implying they must always remain empty strings. This causes the error.

Additionally, using { [key: string]: '' } allows for any string keys. While suitable for arbitrary object states (where you could use Record<string, string>), in most cases stricter typing is preferred. Hence, you should opt for this instead:

<typeof initialState>

But worry not, since TypeScript handles the heavy lifting for you, simply utilize:

const [selected, setSelected] = useState(initialState);

Answer 2

Here is a more effective way to express the same concept:

const initialState = { name: '', gender: '', height: '', weight: '' };
const [selected, setSelected] = useState<typeof initialState>(initialState);

The issue with your method lies in how TypeScript interprets the type and how you envision it to be.

You seem to believe that the inferred type looks like this:

{ [key: string]: '' }

This indicates that any key can be used but only with an empty string value i.e. ''.

However, TypeScript typically infers it differently (which aligns more with common practice) as shown below:

{
    name: string;
    gender: string;
    height: string;
    weight: string;
}

Therefore, when you declare,

const [selected, setSelected] = useState<{ [key: string]: '' }>(initialState);

You are assigning a broader type to a narrower one. TypeScript assumes that the values in initialState can have a string type while you are implying they must always remain empty strings. This causes the error.

Additionally, using { [key: string]: '' } allows for any string keys. While suitable for arbitrary object states (where you could use Record<string, string>), in most cases stricter typing is preferred. Hence, you should opt for this instead:

<typeof initialState>

But worry not, since TypeScript handles the heavy lifting for you, simply utilize:

const [selected, setSelected] = useState(initialState);

What steps can be taken to troubleshoot the "error is not assignable to parameter of type" issue in

Answer №1

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