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setState causing infinite loop in custom hook

I've created a custom hook within my React app, but for some reason when I update the internal state via an event listener, it causes an infinite loop to be triggered (when it shouldn't). Here's my code:
// Note that this isn't a React component - just a regular JavaScript class.
class Player{
static #audio = new Audio();
static #listenersStarted = false;
static #listenerCallbacks = {
playing: [],
paused: [],
loaded: []
};
static mount(){
const loaded = () => {
this.removeListenerCallback("loaded", loaded);
};
this.addListenerCallback("loaded", loaded);
}
// This method is called on the initialization of the React
// app and is only called once. It's only purpose is to ensure
// that all of the listeners and their callbacks get fired.
static startListeners(){
const eventShorthands = {
playing: "play playing",
paused: "pause ended",
loaded: "loadedmetadata"
};
Object.keys(eventShorthands).forEach(key => {
const actualEvents = eventShorthands[key];
actualEvents.split(" ").forEach(actualEvent => {
this.#audio.addEventListener(actualEvent, e => {
const callbacks = this.#listenerCallbacks[key];
callbacks.forEach(callback => {
callback(e)
});
});
});
});
}
static addListenerCallback(event, callback){
const callbacks = this.#listenerCallbacks;
if(callbacks.hasOwnProperty(event)){
// Remember this console log
console.log(true);
this.#listenerCallbacks[event].push(callback);
}
}
static removeListenerCallback(event, callback){
const listenerCallbacks = this.#listenerCallbacks;
if(listenerCallbacks.hasOwnProperty(event)){
const index = listenerCallbacks[event].indexOf(callback);
this.#listenerCallbacks[event].splice(index, 1);
}
}
}
const usePlayer = (slug) => {
// State setup
const [state, setState] = useReducer(
(state, newState) => ({ ...state, ...newState }), {
mounted: false,
animationRunning: false,
allowNextFrame: false
}
);
const _handleLoadedMetadata = () => {
// If I remove this _stopAnimation, the console log mentioned
// in the player class only logs true to the console 5 times.
// Whereas if I keep it, it will log true infinitely.
_stopAnimation();
};
const _stopAnimation = () => {
setState({
allowNextFrame: false,
animationRunning: false
});
}
useEffect(() => {
Player.addListenerCallback("loaded", _handleLoadedMetadata);
return () => {
Player.removeListenerCallback("loaded", _handleLoadedMetadata);
};
}, []);
return {
mounted: state.mounted
};
};
This makes me think that the component keeps on re-rendering and calling Player.addListenerCallback(), but the strange thing is, if I put a console.log(true) within the useEffect() at the end, it'll only output it twice.
All help is appreciated, cheers.

When you're hooking (pun unintended) up inner functions in React components (or hooks) to external event handlers, you'll want to be mindful of the fact that the inner function's identity changes on every render unless you use useCallback() (which is a specialization of useMemo) to guide React to keep a reference to it between renders.
Here's a small simplification/refactoring of your code that seems to work with no infinite loops.
instead of a class with only static members, Player is a regular class of which there is an app-wide singletonesque instance.
instead of hooking up separate event listeners for each event, the often-overlooked handleEvent protocol for addEventListener is used
the hook event listener callback is now properly useCallbacked.
the hook event listener callback is responsible for looking at the event.type field to figure out what's happening.
the useEffect now properly has the ref to the callback it registers/unregisters, so if the identity of the callback does change, it gets properly re-registered.
I wasn't sure what the state in your hook was used for, so it's not here (but I'd recommend three separate state atoms instead of (ab)using useDispatch for an object state if possible).
The same code is here in a Codesandbox (with a base64-encoded example mp3 that I didn't care to add here for brevity).
const SMALL_MP3 = "https://...";
class Player {
#audio = new Audio();
#eventListeners = [];
constructor() {
["play", "playing", "pause", "ended", "loadedmetadata", "canplay"].forEach((event) => {
this.#audio.addEventListener(event, this);
});
}
play(src) {
if (!this.#audio.parentNode) {
document.body.appendChild(this.#audio);
}
this.#audio.src = src;
}
handleEvent = (event) => {
this.#eventListeners.forEach((listener) => listener(event));
};
addListenerCallback(callback) {
this.#eventListeners.push(callback);
}
removeListenerCallback(callback) {
this.#eventListeners = this.#eventListeners.filter((c) => c !== callback);
}
}
const player = new Player();
const usePlayer = (slug) => {
const eventHandler = React.useCallback(
(event) => {
console.log("slug:", slug, "event:", event.type);
},
[slug],
);
React.useEffect(() => {
player.addListenerCallback(eventHandler);
return () => player.removeListenerCallback(eventHandler);
}, [eventHandler]);
};
export default function App() {
usePlayer("floop");
const handlePlay = React.useCallback(() => {
player.play(SMALL_MP3);
}, []);
return (
<div className="App">
<button onClick={handlePlay}>Set player source</button>
</div>
);
}
The output, when one clicks on the button, is
slug: floop event: loadedmetadata
slug: floop event: canplay

How do I use axios response in different components without using export?

As the tittle says, I would like to be able to use the same axios response for differents components.
I have some restrictions like, I'm onlyl able to use react by adding scripts tags to my html so things like exports or jsx are impossible for me.
This is my react code:
class User extends React.Component {
state = {
user: {}
}
componentWillMount() {
console.log(localStorage.getItem("user"))
axios.get('http://localhost:8080/dashboard?user=' + localStorage.getItem("user"))
.then(res => {
const userResponse = res.data
setTimeout(() =>
this.setState({user: userResponse.user}), 1000);
})
}
render () {
const {user} = this.state
if (user.fullName === undefined)
return React.createElement("div", null, 'loading..');
return React.createElement("span", {className: "mr-2 d-none d-lg-inline text-gray-600 small" }, user.fullName);
}
}
ReactDOM.render( React.createElement(User, {}, null), document.getElementById('userDropdown') );
class Roles extends React.Component{
state = {
user: {}
}
componentWillMount() {
console.log(localStorage.getItem("user"))
axios.get('http://localhost:8080/dashboard?user=' + localStorage.getItem("user"))
.then(res => {
const userResponse = res.data
setTimeout(() =>
this.setState({user: userResponse.user}), 1000);
})
}
render () {
const {user} = this.state
const roles = user.user.roles.map((rol) => rol.roleName)
if (user.fullName === undefined)
return React.createElement("div", null, 'loading..');
return React.createElement("a", {className: "dropdown-item" }, user.fullName);
}
}
ReactDOM.render( React.createElement(Roles, {}, null), document.getElementById('dropdownRol') );
I would like to be able to manage different components(rendering each one) with data of the same axios response.
Is this possible considering my limitations?
Thanks in advance

Here's a working example of how you might do it. I've tried to annotate everything with comments, but I'm happy to try to clarify if you have questions.
// Fake response object for the store's "load" request
const fakeResponse = {
user: {
fullName: "Carolina Ponce",
roles: [
{ roleName: "administrator" },
{ roleName: "editor" },
{ roleName: "moderator" },
{ roleName: "generally awesome person" }
]
}
};
// this class is responsible for loading the data
// and making it available to other components.
// we'll create a singleton for this example, but
// it might make sense to have more than one instance
// for other use cases.
class UserStore {
constructor() {
// kick off the data load upon instantiation
this.load();
}
// statically available singleton instance.
// not accessed outside the UserStore class itself
static instance = new this();
// UserStore.connect creates a higher-order component
// that provides a 'store' prop and automatically updates
// the connected component when the store changes. in this
// example the only change occurs when the data loads, but
// it could be extended for other uses.
static connect = function(Component) {
// get the UserStore instance to pass as a prop
const store = this.instance;
// return a new higher-order component that wraps the connected one.
return class Connected extends React.Component {
// when the store changes just force a re-render of the component
onStoreChange = () => this.forceUpdate();
// listen for store changes on mount
componentWillMount = () => store.listen(this.onStoreChange);
// stop listening for store changes when we unmount
componentWillUnmount = () => store.unlisten(this.onStoreChange);
render() {
// render the connected component with an additional 'store' prop
return React.createElement(Component, { store });
}
};
};
// The following listen, unlisten, and onChange methods would
// normally be achieved by having UserStore extend EventEmitter
// instead of re-inventing it, but I wasn't sure whether EventEmitter
// would be available to you given your build restrictions.
// Adds a listener function to be invoked when the store changes.
// Called by componentWillMount for connected components so they
// get updated when data loads, etc.
// The store just keeps a simple array of listener functions. This
// method creates the array if it doesn't already exist, and
// adds the new function (fn) to the array.
listen = fn => (this.listeners = [...(this.listeners || []), fn]);
// Remove a listener; the inverse of listen.
// Invoked by componentWillUnmount to disconnect from the store and
// stop receiving change notifications. We don't want to attempt to
// update unmounted components.
unlisten = fn => {
// get this.listeners
const { listeners = [] } = this;
// delete the specified function from the array.
// array.splice modifies the original array so we don't
// need to reassign it to this.listeners or anything.
listeners.splice(listeners.indexOf(fn), 1);
};
// Invoke all the listener functions when the store changes.
// (onChange is invoked by the load method below)
onChange = () => (this.listeners || []).forEach(fn => fn());
// do whatever data loading you need to do here, then
// invoke this.onChange to update connected components.
async load() {
// the loading and loaded fields aren't used by the connected
// components in this example. just including them as food
// for thought. components could rely on these explicit fields
// for store status instead of pivoting on the presence of the
// data.user object, which is what the User and Role components
// are doing (below) in this example.
this.loaded = false;
this.loading = true;
try {
// faking the data request. wait two seconds and return our
// hard-coded data from above.
// (Replace this with your network fetch.)
this.data = await new Promise(fulfill =>
setTimeout(() => fulfill(fakeResponse), 2000)
);
// update the loading/loaded status fields
this.loaded = true;
this.loading = false;
// call onChange to trigger component updates.
this.onChange();
} catch (e) {
// If something blows up during the network request,
// make the error available to connected components
// as store.error so they can display an error message
// or a retry button or whatever.
this.error = e;
}
}
}
// With all the loading logic in the store, we can
// use a much simpler function component to render
// the user's name.
// (This component gets connected to the store in the
// React.createElement call below.)
function User({ store }) {
const { data: { user } = {} } = store || {};
return React.createElement(
"span",
{ className: "mr-2 d-none d-lg-inline text-gray-600 small" },
user ? user.fullName : "loading (User)…"
);
}
ReactDOM.render(
// Connect the User component to the store via UserStore.connect(User)
React.createElement(UserStore.connect(User), {}, null),
document.getElementById("userDropdown")
);
// Again, with all the data loading in the store, we can
// use a much simpler functional component to render the
// roles. (You may still need a class if you need it to do
// other stuff, but this is all we need for this example.)
function Roles({ store }) {
// get the info from the store prop
const { data: { user } = {}, loaded, loading, error } = store || {};
// handle store errors
if (error) {
return React.createElement("div", null, "oh noes!");
}
// store not loaded yet?
if (!loaded || loading) {
return React.createElement("div", null, "loading (Roles)…");
}
// if we made it this far, we have user data. do your thing.
const roles = user.roles.map(rol => rol.roleName);
return React.createElement(
"a",
{ className: "dropdown-item" },
roles.join(", ")
);
}
ReactDOM.render(
// connect the Roles component to the store like before
React.createElement(UserStore.connect(Roles), {}, null),
document.getElementById("dropdownRol")
);
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script>
<div id="userDropdown"></div>
<div id="dropdownRol"></div>

How do I test `image.onload` using jest in the context of redux actions (or other callbacks assigned in the action)

My problem was that I am trying to make a unit test for a function but can't figure out how to test a part of it.
This is a react / redux action that does the following:
1) retrieves json data with an image url
2) loads the image into an Image instance and dispatches its size to the reducer (asynchronously when image is loaded using Image.onload)
3) dispatches that the fetch was completed to the reducer
The image onload happens asynchronously, so when I try to unit test it it wouldn't be called. Moreover, I can't just mock things out because the image instance is created within the function...
Here's the code I wanted to test (removing some checks, branching logic, and stuff):
export function fetchInsuranceCardPhoto() {
return dispatch => {
dispatch(requestingInsuranceCardPhoto());
return fetch(`${api}`,
{
headers: {},
credentials: 'same-origin',
method: 'GET',
})
.then(response => {
switch (response.status) {
case 200:
return response.json()
.then(json => {
dispatch(receivedInsuranceCardPhoto(json));
})
}
});
};
}
function receivedInsuranceCardPhoto(json) {
return dispatch => {
const insuranceCardFrontImg = json.insuranceCardData.url_front;
const insuranceCardBackImg = json.insuranceCardData.url_back;
if (insuranceCardFrontImg) {
dispatch(storeImageSize(insuranceCardFrontImg, 'insuranceCardFront'));
}
return dispatch(receivedInsuranceCardPhotoSuccess(json));
};
}
function receivedInsuranceCardPhotoSuccess(json) {
const insuranceCardFrontImg = json.insuranceCardData.url_front;
const insuranceCardBackImg = json.insuranceCardData.url_back;
const insuranceCardId = json.insuranceCardData.id;
return {
type: RECEIVED_INSURANCE_CARD_PHOTO,
insuranceCardFrontImg,
insuranceCardBackImg,
insuranceCardId,
};
}
function storeImageSize(imgSrc, side) {
return dispatch => {
const img = new Image();
img.src = imgSrc;
img.onload = () => {
return dispatch({
type: STORE_CARD_IMAGE_SIZE,
side,
width: img.naturalWidth,
height: img.naturalHeight,
});
};
};
}
Notice in that last storeImageSize private function how there's an instance of Image created and an image.onload that is assigned to a function.
Now here's my test:
it('triggers RECEIVED_INSURANCE_CARD_PHOTO when 200 returned without data', async () => {
givenAPICallSucceedsWithData();
await store.dispatch(fetchInsuranceCardPhoto());
expectActionsToHaveBeenTriggered(
REQUESTING_INSURANCE_CARD_PHOTO,
RECEIVED_INSURANCE_CARD_PHOTO,
STORE_CARD_IMAGE_SIZE,
);
});
This test though will fail because the test finishes before the image.onload callback is called.
How can I force the image.onload callback to be called so that I can test that the `STORE_CARD_IMAGE_SIZE action gets broadcasted?

After some investigation, I found a very interesting javascript function that would solve my issue.
It is this: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperty
Here's how I used Object.defineProperty(...) to solve my issue:
describe('fetchInsuranceCardPhoto', () => {
let imageOnload = null;
/** Override Image global to save onload setting here so that I can trigger it manually in my test */
function trackImageOnload() {
Object.defineProperty(Image.prototype, 'onload', {
get: function () {
return this._onload;
},
set: function (fn) {
imageOnload = fn;
this._onload = fn;
},
});
}
it('triggers RECEIVED_INSURANCE_CARD_PHOTO when 200 returned with data', async () => {
trackImageOnload();
givenAPICallSucceedsWithData();
await store.dispatch(fetchInsuranceCardPhoto());
imageOnload();
expectActionsToHaveBeenTriggered(
REQUESTING_INSURANCE_CARD_PHOTO,
RECEIVED_INSURANCE_CARD_PHOTO,
STORE_CARD_IMAGE_SIZE,
);
});
What I did here was use define property to override the setter of any instance of Image. the setter would continue to get or set like normal but would also save the value (in this case a function) that was set to a variable in the scope of the unit test. After which, you can just run that function you captured before the verification step of your the test.
Gotchas
- configurable needs to be set
- note that defineProperty is a different function than defineProperties
- This is bad practice in real code.
- remember to use the prototype
Hope this post can help a dev in need!

Redux updateElementSaga has been cancelled. Why?

I just implemented a drag and drop feature with react-dnd and when the user drops the SkyElement item in my app, I update top and left on the server which in turn updates the redux store
However, the update call works occasionally, not every time. And in my console, I see a warning; updateElementSaga has been cancelled
In my SlotView.js, in a function, I have:
this.props.dispatch(requestUpdateElement({ id, top, left }));
In my elements/actions.js:
export function requestUpdateElement(element) {
return { type: 'requestUpdateElement', element };
}
In my elements/sagas.js:
export function *updateElementSaga(action) {
const response = yield call(api.updateElement, action.element);
if (response.element) {
// debugger; // this hits, saga was cancelled will have appeared in the console at this point
yield put(actions.receiveElement(response.element));
} else if (response.error) {
console.log('error receiving element');
}
}
export default [
takeLatest('requestUpdateElement', updateElementSaga),
];
In api.js:
export function updateElement(element) {
const userId = JSON.parse(localStorage.cookies).userId;
element.userId = userId;
if (userId) {
return apiHelper.put(
`${apiHelper.getBaseUrl()}/users/${element.userId}/elements/${element.id}`,
{element},
{headers: apiHelper.getHeaders()}
).catch((error) => {
return {error};
});
} else {
console.log('user ID could not be found for request');
}
}
And my elements/reducer.js:
const defaultState = {
elementsMap: {},
visibleElements: [],
unplacedElements: [],
};
export default function(state = defaultState, action) {
switch (action.type) {
case 'receiveElement':
let element = null;
let unplacedElement = null;
if (action.element.sectorId === undefined) {
unplacedElement = `${action.element.id}`;
} else {
element = `${action.element.id}`;
// don't add, duplicate
const newState = {...state}; // copy old state
delete newState[`${action.element.id}`]; // delete the item from the object
const newVisibleElements = newState.visibleElements.filter(e => e !== `${action.element.id}`); // remove item from visible elements
const newUnplacedElements = newState.unplacedElements.filter(e => e !== `${action.element.id}`);
return {
...newState,
elementsMap: {
...newState.elementsMap,
[element]: action.element,
},
visibleElements: [...newVisibleElements, element],
unplacedElements: [...newUnplacedElements],
};
}
return {
...state,
elementsMap: {
...state.elementsMap,
[action.element.id]: action.element,
},
visibleElements: [...state.visibleElements, element],
unplacedElements: [...state.unplacedElements, unplacedElement],
};
default:
return state;
}
}
Like I mentioned before, sometimes the update works, but not every time. I've narrowed the problem down to the client. Server seems to be acting fine. Any idea what I'm doing wrong here? Thanks!

If you are using takeLatest the redux saga documentation does mention:
https://redux-saga.js.org/docs/basics/UsingSagaHelpers.html
Unlike takeEvery, takeLatest allows only one fetchData task to run at
any moment. And it will be the latest started task. If a previous
task is still running when another fetchData task is started, the
previous task will be automatically cancelled.
Where fetchData is the generator function that is being served using takeLatest or takeEvery
And when your UI keeps invoking the same action, before it gets completed, it will keep cancelling
the last invoked action, and hence you would keep getting the message intermittently:
updateElementSaga has been cancelled
Which by nature takeLatest is doing the right thing. Which is:
Always take the latest invoked action
In case you want every action to be caught and processed, do use takeEvery, as:
export default [
takeEvery('requestUpdateElement', updateElementSaga),
];

How to write state changing routine, similar to Redux?

How can I write a really super, simple state changing routine? I need something like Redux, but way simpler, don't need all the bells & whistles.
I was thinking of a global object i.e. myState = {}, that is changed via setMyState() / getMyState().
I'm using JavaScript, and wondering if this would be done via a timer that polls say every 10ms, or so.
So in my JavaScript client app (I'm using ReactJS), a call to my getMyState("show-menu") inside a render() would update the Component's state just like using this.state..
The reason I want this is:
1) Wanna know how to write it for learning purposes.
2) Need something simpler that Redux, simple like Meteor's Session vars, so don't have to pass this.Refs. down to child compnents which setState on parent components.
3) Redux is a mouthful, there is still lots to digest and learn to use Redux.

Seems like you could do this pretty simply with a constructor.
function State () {
this._state = {};
...
}
State.prototype.get = function () {
return this._state;
};
State.prototype.set = function (state) {
return this._state = state;
};
var STATE = new State();
But then you have to do the polling you mentioned in your post. Alternatively, you can look at eventEmitter libraries for javascript, for example https://github.com/facebook/emitter, and turn the State object into an event emitter.

Update
Not sure if this is what you're looking for, at all, but it's simpler.
function makeStore () {
var state = { };
return {
set (key, value) { state[key] = value; },
get (key) { return state[key]; }
};
}
const store = makeStore();
store.set("counter", 1);
store.get("counter"); // 1
Believe it or not, there's really not a lot to Redux.
There's, perhaps, a lot to think about, and it's extra work to keep everything untied from your store...
But have a quick look:
function reducer (state, action) {
state = state || { count: 0 };
const direction = (action.type === "INCREASE") ? 1 : (action.type === "DECREASE") ? -1 : 0;
return {
count: (state.count + direction)
};
}
function announceState () {
console.log(store.getState());
}
function updateView () {
const count = store.getState().count;
document.querySelector("#Output").value = count || 0;
}
function increase () {
store.dispatch({ type: "INCREASE" });
}
function decrease () {
store.dispatch({ type: "DECREASE" });
}
const store = createStore(reducer, { count: 0 });
store.subscribe(announceState)
.subscribe(updateView);
document.querySelector("#Increment").onclick = increase;
document.querySelector("#Decrement").onclick = decrease;
updateView();
This is the code I intend to use.
Looking at it, I'm pretty much just creating a store (with a function to run every time there's an event), there's the subscription to have a listener run, after the store has updated, there's a line where I fire an action, and... ...well, that's it.
function createStore (reduce, initialState) {
var state = initialState;
var listeners = [];
function notifyAll () {
listeners.forEach(update => update());
}
function dispatch (event) {
const newState = reduce(state, event);
state = newState;
notifyAll();
return store;
}
function subscribe (listener) {
listeners.push(listener);
return store;
}
function getState () {
return state;
}
const store = {
getState, subscribe, dispatch
};
return store;
}
// THIS IS MY APPLICATION CODE
function reducer (state, action) {
state = state || { count: 0 };
const direction = (action.type === "INCREASE") ? 1 : (action.type === "DECREASE") ? -1 : 0;
return {
count: (state.count + direction)
};
}
function announceState () {
console.log(store.getState());
}
function updateView () {
const count = store.getState().count;
document.querySelector("#Output").value = count || 0;
}
function increase () {
store.dispatch({ type: "INCREASE" });
}
function decrease () {
store.dispatch({ type: "DECREASE" });
}
const store = createStore(reducer, { count: 0 });
store.subscribe(announceState)
.subscribe(updateView);
document.querySelector("#Increment").onclick = increase;
document.querySelector("#Decrement").onclick = decrease;
updateView();
<button id="Decrement">-</button>
<output id="Output"></output>
<button id="Increment">+</button>
The very tiny, very easy implementation of a store (note that the real thing is more complex) is above. dispatch and subscribe are very useful, here.