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How do i return an object from my react state

I am trying to find an item from a collection, from the code below, in order to update my react component, the propertState object isnt empty, it contains a list which i have console logged, however I seem to get an underfined object when i console log the value returned from my findProperty function... I am trying update my localState with that value so that my component can render the right data.
const PropertyComponent = () => {
const { propertyId } = useParams();
const propertyState: IPropertiesState = useSelector(
propertiesStateSelector
);
const[property, setProperty] = useState()
const findProperty = (propertyId, properties) => {
let propertyReturn;
for (var i=0; i < properties.length; i++) {
if (properties[i].propertyId === propertyId) {
propertyToReturn = properties[i];
break;
}
}
setProperty(propertyReturn)
return propertyReturn;
}
const foundProperty = findProperty(propertyId, propertyState.properties);
return (<>{property.propertyName}</>)
}
export default PropertyComponent

There are a few things that you shall consider when you are finding data and updating states based on external sources of data --useParams--
I will try to explain the solution by dividing your code in small pieces
const PropertyComponent = () => {
const { propertyId } = useParams();
Piece A: Consider that useParams is a hook connected to the router, that means that you component might be reactive and will change every time that a param changes in the URL. Your param might be undefined or an string depending if the param is present in your URL
const propertyState: IPropertiesState = useSelector(
propertiesStateSelector
);
Piece B: useSelector is other property that will make your component reactive to changes related to that selector. Your selector might return undefined or something based on your selection logic.
const[property, setProperty] = useState()
Piece C: Your state that starts as undefined in the first render.
So far we have just discovered 3 pieces of code that might start as undefined or not.
const findProperty = (propertyId, properties) => {
let propertyReturn;
for (var i=0; i < properties.length; i++) {
if (properties[i].propertyId === propertyId) {
propertyToReturn = properties[i];
break;
}
}
setProperty(propertyReturn)
return propertyReturn;
}
const foundProperty = findProperty(propertyId, propertyState.properties);
Piece D: Here is where more problems start appearing, you are telling your code that in every render a function findProperty will be created and inside of it you are calling the setter of your state --setProperty--, generating an internal dependency.
I would suggest to think about the actions that you want to do in simple steps and then you can understand where each piece of code belongs to where.
Let's subdivide this last piece of code --Piece D-- but in steps, you want to:
Find something.
The find should happen if you have an array where to find and a property.
With the result I want to notify my component that something was found.
Step 1 and 2 can happen in a function defined outside of your component:
const findProperty = (propertyId, properties) => properties.find((property) => property.propertyId === propertyId)
NOTE: I took the liberty of modify your code by simplifying a little
bit your find function.
Now we need to do the most important step, make your component react at the right time
const findProperty = (propertyId, properties) => properties.find((property) => property.propertyId === propertyId)
const PropertyComponent = () => {
const { propertyId } = useParams();
const propertyState: IPropertiesState = useSelector(
propertiesStateSelector
);
const[property, setProperty] = useState({ propertyName: '' }); // I suggest to add default values to have more predictable returns in your component
/**
* Here is where the magic begins and we try to mix all of our values in a consistent way (thinking on the previous pieces and the potential "undefined" values) We need to tell react "do something when the data is ready", for that reason we will use an effect
*/
useEffect(() => {
// This effect will run every time that the dependencies --second argument-- changes, then you react afterwards.
if(propertyId, propertyState.properties) {
const propertyFound = findProperty(propertyId, propertyState.properties);
if(propertyFound){ // Only if we have a result we will update our state.
setProperty(propertyFound);
}
}
}, [propertyId, propertyState.properties])
return (<>{property.propertyName}</>)
}
export default PropertyComponent
I think that in this way your intention might be more direct, but for sure there are other ways to do this. Depending of your intentions your code should be different, for instance I have a question:
What is it the purpose of this component? If its just for getting the property you could do a derived state, a little bit more complex selector. E.G.
function propertySelectorById(id) {
return function(store) {
const allProperties = propertiesStateSelector(store);
const foundProperty = findProperty(id, allProperties);
if( foundProperty ) {
return foundProperty;
} else {
return null; // Or empty object, up to you
}
}
}
Then you can use it in any component that uses the useParam, or just create a simple hook. E.G.
function usePropertySelectorHook() {
const { propertyId } = useParams();
const property = useSelector(propertySelectorById(propertyId));
return property;
}
And afterwards you can use this in any component
functon AnyComponent() {
const property = usePropertySelectorHook();
return <div> Magic {property}</div>
}
NOTE: I didn't test all the code, I wrote it directly in the comment but I think that should work.
Like this I think that there are even more ways to solve this, but its enough for now, hope that this helped you.

do you try this:
const found = propertyState.properties.find(element => element.propertyId === propertyId);
setProperty(found);
instead of all function findProperty

React state: unable to get updated value inside onChange

I am using an array of components that are interested depending on various conditions i.e the order and number of elements in the array are dynamic as shown below:
useEffect(() => {
const comp = [];
// if(condition1===true){
comp.push(<MyComp onChange={onValueChange} />);
// }
// if(condition2===true){
comp.push(<YourComp onChange={onValueChange} />);
// }
// if(condition3===true){
comp.push(<HisComp onChange={onValueChange} />);
// }
setComponents(comp);
}, []);
To each of the components in the array, there could be some sort of input control like input-text, input-number, text-area, chips, radio, checkbox, etc.
So there is an onChange event linked to each of these components.
I am using a common onValueChange function which is passed as a callback to these components. In the onValueChange I need 2 things:
changed value (from child component)
activeIndex (from same component)
const onValueChange = (val) => {
console.log("onChange Valled", val, "activeIndex==", activeIndex);
};
But here I am not able to fetch the updated value on activeIndex, it always gives zero no matter in what active step I am in.
Sandbox DEMO

useEffect(() => {
setComponents((previousValues)=>{
// if you want to add on previous state
const comp = [...previousValues];
// if you want to overwrite previous state
const comp = [];
if(condition1===true){
comp.push();
}
if(condition2===true){
comp.push();
}
if(condition3===true){
comp.push();
}
return comp;
});
}, []);

Try using useCallback with dependency array. Also try to avoid storing components in state - the office advice - what shouldn’t go in state?
const onValueChange = useCallback((val) => {
console.log("onChange Valled", val, "activeIndex==", activeIndex);
},[activeIndex];
For rendering try something like below.
condition1===true && <MyComp onChange={onValueChange} />
or create a function which returns the component eg: getComponent(condition) and use this in render/return. Make sure you wrap getComponent in useCallback with empty dependency array []

How to fix scope problem inside "then" function react?

I am trying to print out of Printer. I am a little new to react and javascript. I am trying to pass the state to a then function of Third Party Code. But i am getting an error:
Cannot read property 'restaurant_name' of undefined
How can i pass state to the scope of then function of qz?
print = () => {
let { state } = this.state;
qz.websocket.connect()
.then(function() {
return qz.printers.find("BillPrinter");
}).then(function(printer) {
var config = qz.configs.create(printer);
var data = [
`${state.restaurant_name}` + '\x0A',
`${state.restaurant_address}`
]
return qz.print(config, data);
});
}

You have some unnecessary destructuring that is causing your error - this.state.state doesn't exist, yet this line:
let { state } = this.state;
Is equivalent to:
let state = this.state.state;
Remove the curly braces and it'll work fine.
let state = this.state;
Also note that state will be a reference to this.state rather than being another object.

Use arrow function to keep the function in the upper scope as #Ali Torki suggested:
.then(printer => {....})

React useState hook event handler using initial state

I'm still getting my head around react hooks but struggling to see what I'm doing wrong here. I have a component for resizing panels, onmousedown of an edge I update a value on state then have an event handler for mousemove which uses this value however it doesn't seem to be updating after the value has changed.
Here is my code:
export default memo(() => {
const [activePoint, setActivePoint] = useState(null); // initial is null
const handleResize = () => {
console.log(activePoint); // is null but should be 'top|bottom|left|right'
};
const resizerMouseDown = (e, point) => {
setActivePoint(point); // setting state as 'top|bottom|left|right'
window.addEventListener('mousemove', handleResize);
window.addEventListener('mouseup', cleanup); // removed for clarity
};
return (
<div className="interfaceResizeHandler">
{resizePoints.map(point => (
<div
key={ point }
className={ `interfaceResizeHandler__resizer interfaceResizeHandler__resizer--${ point }` }
onMouseDown={ e => resizerMouseDown(e, point) }
/>
))}
</div>
);
});
The problem is with the handleResize function, this should be using the latest version of activePoint which would be a string top|left|bottom|right but instead is null.

How to Fix a Stale useState
Currently, your issue is that you're reading a value from the past. When you define handleResize it belongs to that render, therefore, when you rerender, nothing happens to the event listener so it still reads the old value from its render.
There are a several ways to solve this. First let's look at the most simple solution.
Create your function in scope
Your event listener for the mouse down event passes the point value to your resizerMouseDown function. That value is the same value that you set your activePoint to, so you can move the definition of your handleResize function into resizerMouseDown and console.log(point). Because this solution is so simple, it cannot account for situations where you need to access your state outside of resizerMouseDown in another context.
See the in-scope function solution live on CodeSandbox.
useRef to read a future value
A more versatile solution would be to create a useRef that you update whenever activePoint changes so that you can read the current value from any stale context.
const [activePoint, _setActivePoint] = React.useState(null);
// Create a ref
const activePointRef = React.useRef(activePoint);
// And create our custom function in place of the original setActivePoint
function setActivePoint(point) {
activePointRef.current = point; // Updates the ref
_setActivePoint(point);
}
function handleResize() {
// Now you'll have access to the up-to-date activePoint when you read from activePointRef.current in a stale context
console.log(activePointRef.current);
}
function resizerMouseDown(event, point) {
/* Truncated */
}
See the useRef solution live on CodeSandbox.
Addendum
It should be noted that these are not the only ways to solve this problem, but these are my preferred methods because the logic is more clear to me despite some of the solutions being longer than other solutions offered. Please use whichever solution you and your team best understand and find to best meet your specific needs; don't forget to document what your code does though.

You have access to current state from setter function, so you could make it:
const handleResize = () => {
setActivePoint(activePoint => {
console.log(activePoint);
return activePoint;
})
};

useRef for the callback
A similar approach to Andria's can be taken by using useRef to update the event listener's callback itself instead of the useState value. This allows you to use many up-to-date useState values inside one callback with only one useRef.
If you create a ref with useRef and update its value to the handleResize callback on every render, the callback stored in the ref will always have access to up-to-date useState values, and the handleResize callback will be accessible to any stale callbacks like event handlers.
function handleResize() {
console.log(activePoint);
}
// Create the ref,
const handleResizeRef = useRef(handleResize);
// and then update it on each re-render.
handleResizeRef.current = handleResize;
// After that, you can access it via handleResizeRef.current like so
window.addEventListener("mousemove", event => handleResizeRef.current());
With this in mind, we can also abstract away the creation and updating of the ref into a custom hook.
Example
See it live on CodeSandbox.
/**
* A custom hook that creates a ref for a function, and updates it on every render.
* The new value is always the same function, but the function's context changes on every render.
*/
function useRefEventListener(fn) {
const fnRef = useRef(fn);
fnRef.current = fn;
return fnRef;
}
export default memo(() => {
const [activePoint, setActivePoint] = useState(null);
// We can use the custom hook declared above
const handleResizeRef = useRefEventListener((event) => {
// The context of this function will be up-to-date on every re-render.
console.log(activePoint);
});
function resizerMouseDown(event, point) {
setActivePoint(point);
// Here we can use the handleResizeRef in our event listener.
function handleResize(event) {
handleResizeRef.current(event);
}
window.addEventListener("mousemove", handleResize);
// cleanup removed for clarity
window.addEventListener("mouseup", cleanup);
}
return (
<div className="interfaceResizeHandler">
{resizePoints.map((point) => (
<div
key={point}
className={`interfaceResizeHandler__resizer interfaceResizeHandler__resizer--${point}`}
onMouseDown={(event) => resizerMouseDown(event, point)}
/>
))}
</div>
);
});

const [activePoint, setActivePoint] = useState(null); // initial is null
const handleResize = () => {
setActivePoint(currentActivePoint => { // call set method to get the value
console.log(currentActivePoint);
return currentActivePoint; // set the same value, so nothing will change
// or a different value, depends on your use case
});
};

Just small addition to the awe ChrisBrownie55's advice.
A custom hook can be implemented to avoid duplicating this code and use this solution almost the same way as the standard useState:
// useReferredState.js
import React from "react";
export default function useReferredState(initialValue) {
const [state, setState] = React.useState(initialValue);
const reference = React.useRef(state);
const setReferredState = value => {
reference.current = value;
setState(value);
};
return [reference, setReferredState];
}
// SomeComponent.js
import React from "react";
const SomeComponent = () => {
const [someValueRef, setSomeValue] = useReferredState();
// console.log(someValueRef.current);
};

For those using typescript, you can use this function:
export const useReferredState = <T>(
initialValue: T = undefined
): [T, React.MutableRefObject<T>, React.Dispatch<T>] => {
const [state, setState] = useState<T>(initialValue);
const reference = useRef<T>(state);
const setReferredState = (value) => {
reference.current = value;
setState(value);
};
return [state, reference, setReferredState];
};
And call it like that:
const [
recordingState,
recordingStateRef,
setRecordingState,
] = useReferredState<{ test: true }>();
and when you call setRecordingState it will automatically update the ref and the state.

You can make use of the useEffect hook and initialise the event listeners every time activePoint changes. This way you can minimise the use of unnecessary refs in your code.

When you need to add event listener on component mount
Use, useEffect() hook
We need to use the useEffect to set event listener and cleanup the same.
The use effect dependency list need to have the state variables which are being used in event handler. This will make sure handler don't access any stale event.
See the following example. We have a simple count state which gets incremented when we click on given button. Keydown event listener prints the same state value. If we remove the count variable from the dependency list, our event listener will print the old value of state.
import { useEffect, useState } from 'react';
function App() {
const [count, setCount] = useState(0);
const clickHandler = () => {
console.log({ count });
setCount(c => c + 1);
}
useEffect(() => {
document.addEventListener('keydown', normalFunction);
//Cleanup function of this hook
return () => {
document.removeEventListener('keydown', normalFunction);
}
}, [count])
return (
<div className="App">
Learn
<button onClick={clickHandler}>Click me</button>
<div>{count}</div>
</div>
);
}
export default App;

Update state with setState ReactJs

I'm trying to update state variable when button click.but my issue is,it's update once with correct data then again it updated with constructor defined data.
constructor(props) {
super(props);
this.state = {
popupshow: [{ check: false, id: '' }]
}
}
componentDidUpdate(prevProps, prevState) {
console.log("this.state.popupshow",this.state.popupshow)
}
Details(type){
this.state.popupshow[i].id = type
this.state.popupshow[i].check = true;
this.setState({ popupshow: this.state.popupshow });
}
render() {
return (
<a onClick={() => this.Details("Tv Series")}>Update </>
)
}
my console.log is like bellow

You should not update React state directly. You should always update/set React state via setState method.
These lines are against React principal
this.state.popupshow[i].id = type
this.state.popupshow[i].check = true;
Update your Details as follows
Details(type){
let { popupshow } = this.state;
let i = 0;
popupshow[i].id = type
popupshow[i].check = true;
this.setState({ popupshow });
}
Note I dont have idea of variable i so assumed that as 0

I think you should rewrite details functions like :
Details(type, i){
const popupDetail = Object.assign([], this.state.popupshow);
popupDetail[i].id = type
popupDetail[i].check = true;
this.setState({ popupshow: popupDetail });
}
you are setting popupshow: this.state.popupshow this is causing forceupdate which re renders the component hence its value gets reset.

I totally agree with the other answers have given for the question, however there are few things worth noting is you might wanna add the function to the context.
The argument in favour of adding these lines to the constructor is so that the new bound functions are only created once per instance of the class. You could also use
onClick={this.Details.bind(this, "Tv Series")}
or (ES6):
onClick={() => this.Details("Tv Series")}
but either of these methods will create a new function every time the component is re-rendered.
Then change the function to arrow fucntion too like
Details(type, i){
const popupDetail = Object.assign([], this.state.popupshow);
popupDetail[i].id = type
popupDetail[i].check = true;
this.setState({ popupshow: popupDetail });
}