useState depending on other state - react-hooks

Question

I have this useSiren hook that should update its state with the incoming json argument but it doesnt.
On the first call the json is an empty object, because the fetch effect has not been run yet.
On the second call its also an empty object (triggered by loading getting set to true in App)
And on the third call its filled with valid data. However, the valid data is not applied. The state keeps its initial value.
I guess somehow setSiren must be called to update it, since initial state can only be set once. But how would I do that? Who should call `setSiren?
import { h, render } from 'https://unpkg.com/preact#latest?module';
import { useEffect, useState, useCallback } from 'https://unpkg.com/preact#latest/hooks/dist/hooks.module.js?module';
import htm from "https://unpkg.com/htm#latest/dist/htm.module.js?module";
const html = htm.bind(h);
function useFetch({
method = "GET",
autoFetch = true,
href,
body
}) {
const [loading, setLoading] = useState(false)
const [error, setError] = useState()
const [response, setResponse] = useState()
const [isCancelled, cancel] = useState()
const [json, setJson] = useState({})
const sendRequest = async payload => {
try {
setLoading(true)
setError(undefined)
const response = await fetch(href.replace("http://", "https://"), {
method
})
const json = await response.json()
if (!isCancelled) {
setJson(json)
setResponse(response)
}
return json
} catch (err) {
if (!isCancelled) {
setError(err)
}
throw err
} finally {
setLoading(false)
}
}
if (autoFetch) {
useEffect(() => {
sendRequest(body)
return () => cancel(true)
}, [])
}
return [{
loading,
response,
error,
json
},
sendRequest
]
}
function useSiren(json) {
const [{ entities = [], actions = [], links, title }, setSiren] = useState(json)
const state = (entities.find(entity => entity.class === "state")) || {}
return [
{
title,
state,
actions
},
setSiren
]
}
function Action(props) {
const [{ loading, error, json }, sendRequest] = useFetch({ autoFetch: false, href: props.href, method: props.method })
const requestAndUpdate = () => {
sendRequest().then(props.onRefresh)
}
return (
html`
<button disabled=${loading} onClick=${requestAndUpdate}>
${props.title}
</button>
`
)
}
function App() {
const [{ loading, json }, sendRequest] = useFetch({ href: "https://restlr.io/toggle/0" })
const [{ state, actions }, setSiren] = useSiren(json)
return (
html`<div>
<div>State: ${loading ? "Loading..." : (state.properties && state.properties.value)}</div>
${actions.map(action => html`<${Action} href=${action.href} title=${action.title || action.name} method=${action.method} onRefresh=${setSiren}/>`)}
<button disabled=${loading} onClick=${sendRequest}>
REFRESH
</button>
</div>
`
);
}
render(html`<${App}/>`, document.body)

Answer 1

Maybe what you want to do is to update the siren state when the json param changes? You can use a useEffect to automatically update it.
function useSiren(json) {
const [{ entities = [], actions = [], links, title }, setSiren] = useState(json)
useEffect(() => { // here
setSiren(json)
}, [json])
const state = (entities.find(entity => entity.class === "state")) || {}
return [
{
title,
state,
actions
},
setSiren
]
}

Answer 2

The pattern mentioned by #awmleer is packaged in use-selector:
import { useSelectorValue } from 'use-selector';
const { entities=[], actions=[], title} = json;
const siren = useSelectorValue(() => ({
state: entities.find(entity => entity.class === 'state') || {},
actions,
title
}), [json]);
Disclosure I'm author and maintainer of use-selector