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Improve specificity of return type #49

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Improve specificity of return type #49

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28 changes: 17 additions & 11 deletions src/usePromise.ts
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Original file line number Diff line number Diff line change
@@ -1,17 +1,23 @@
import { useEffect, useState, useRef } from 'react'

type PromiseState<T> = {
loading: true
error: null
value: undefined
} | {
loading: false
error: null
value: T
} | {
loading: false
error: Error
value: undefined
};

export default function usePromise<T>(
promiseOrFn: (() => Promise<T>) | Promise<T>
): {
loading: boolean
error: Error | null
value: T | undefined
} {
const [state, setState] = useState<{
loading: boolean
error: Error | null
value: T | undefined
}>({
): PromiseState<T> {
const [state, setState] = useState<PromiseState<T>>({
loading: !!promiseOrFn,
error: null,
value: undefined
Expand All @@ -22,7 +28,7 @@ export default function usePromise<T>(
if (!promiseOrFn) {
setState({
loading: false,
error: null,
error: new TypeError(`The argument passed to usePromise must be either a promise or a function, but you passed a ${typeof promiseOrFn}`),
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Alternatively, this could throw a type error instead b/c a falsy value in promiseOrFn doesn't satisfy the type specified for the hook argument. Throwing an error might be better than setting an error on the state since this has the potential to be incorrectly interpreted as a rejected promise. 🤷 Would like your input on this please.

value: undefined
})
} else {
Expand Down