TypeScript can often infer the type of a useState hook. For instance, in the following example, TypeScript infers a type of boolean:
const [open, setOpen] = React.useState(false);If we have a useState hook that can be null or a string:
const [error, setError] = React.useState(null);
setError('There was an error');
// Argument of type 'string' is not assignable
// to parameter of type 'SetStateAction<null>'then we'll get a TypeScript warning when we violate the inferred type of
SetStateAction<null>.
The useState can be appropriate typed for this situation like so:
const [error, setError] =
React.useState<null | string>(null);