React state undefined in function. React state variable value appearing to be null.

React state undefined in function When it prints values it is when the setIterval is executing the function, and it prints undefined when the function is not called (meanwhile) Dec 1, 2021 · Type 'Event[] | undefined' is not an array type. Here is my code: The setState function is native to the React. Functional Components(like you used) Class Components; Functional Components are stateless(in older versions, you can use hooks now) components. js returns undefined. Here is a minimal example: const A = () =&gt; { const [value, function typeContactGetter is binded to this and everything is working, the only issue is in the functions return on the &lt;li&gt; element, I am trying to set a className coming from state and it 1. useState() undefined in React just after set. ts(2461) (parameter) prevState: Event[] | undefined When I forgo the state update function inside the useEffect and just set 'Hierarchy' to the 'selectedEvent', it does set that single event to the hierarchy, but obviously I need more than that. 0. componentDidMount() is called after the component is rendered, so inside the render() function it will be undefined. js file. Nov 22, 2018 · However, this. console. State is immutable in terms of a single render; therefore you'll never get the updated state until the next render. I already found this question on SO and added the suggested code to my constructor: class Game extends React. Mar 16, 2019 · This boils down to how closures work in JavaScript. As a final example, say we are calling a function right after trying to mutate our state, but this function depends on the state value. path && this. listOfUsers. /Flashcard. Accessing the state inside the return body works fine. songBuilder--works as this point to current object. – Jul 26, 2015 · I currently have this component in React. log(props) const Image = styled. In this case you haven't set a default for Product so it is undefined. Feb 14, 2016 · Playing with react, trying to build a simple chat app that will be connected to firebase. css' import { Button, } from '@material-ui/core'; function Flas Feb 28, 2020 · The solution I found was to set the state in the getProducts function like setProducts(previousProducts => ( react state is undefined inside the function. companies, }); } you update state. Jul 9, 2022 · Please try the below, it has the update that the component class extends React. state' being undefined. Do not set state by direct definition as you are throughout your code (ex. ChatApp -> import React from 'react'; import Jul 12, 2020 · Hello everyone, I am trying to create an add to cart function that takes a product from a page and adds the properties to an array. Dec 28, 2019 · I'm new to react so I'm sure I'm missing something basic. speak(). Dec 30, 2015 · Furthermore I fetch initial state parameters from the sever through the componentDidMount function. This. Then we check the event object for whatever target element name that fired the function (which The lack of default or “empty state” data can bite you another way, too: when undefined state is passed as a prop to a child component. Sep 1, 2017 · addUser = (userName) => { console. It is a special function that allows you to manage state within functional components without the need for class-based components. I am working to achieve the funcionaity where the &quot;main-page&quot; checks for auth, and if auth is &quot;false&quot; , it redirects to the &quot; Jul 15, 2018 · Uncaught (in promise) TypeError: this. Dec 30, 2020 · I'm still learning react. state. setState is not a function React. searchMode) However, if we log it now you will get a stale value of this. firstSong. If your function is defined within an object, calling it directly from an object will set its context to the object on which the function is being called. A change in the ref will not trigger a re-render. state is undefined. gameState. However, setState accepts a callback in the second parameter that will be called after the setState is complete so you can log the new state. Aug 23, 2021 · However, I cannot pass null as the <select /> value due to the expected TS props on the select component as it expects to receive <IUser['id'][] | undefined>. Apr 1, 2020 · React hooks state undefined on handle function. setState({ users: this. Sep 15, 2021 · When used with function calls, it returns undefined if the given function does not exist. Apr 2, 2020 · React Quill calls onChange() with 4 args: html, delta, source, editor: 1 html: the editor contents in HTML format, a string 2 delta: the editor contents as a Delta object, Quill's internal and recommended format Jun 5, 2020 · The issue is that when the component renders the first time the axios request hasn't finished running. ReactJs this. Warning: Can't call setState (or forceUpdate) on an unmounted component. So instead of doing. You can use an effect to log the value when it updates. React puts your updater functions in a queue. My component structure looks something like this: <App> <Modal Lauch Button /> <Modal> <Modal Header /> <Modal Body /> <-- here's the problem </Modal> </App> and my initial state array is of the form (of course JSON encoded): Jun 1, 2017 · From here, you maintain your state by using React's build in setState function (read about it more in the documentation here). path); } May 11, 2016 · I'm having trouble accessing this. menuSelected) Or, and here comes my suggestion , move createMenuItems outside of render method: May 14, 2021 · In this post we discovered why React class components might appear to have undefined state and a few different ways to solve the issue. 1. log executes. React Hook useState Is Returning Undefined. log('render', this. jsx Setting state is asynchronous so you won't see the updated state in the console log that is really right after the set state. Mar 29, 2020 · I'm new to React Hooks. This is because you are calling groupByCategory within the initial value you're assigning to this. Nov 25, 2017 · Glad to hear it. useRef(). async function foo() {await updateState(); // Execution pauses Your getUserInfos function doesn't have return xyz anywhere (one of the axios callback functions does, but not getUserInfos). React State returning Undefined. state property is See full list on typeofnan. where a function (here setCity, setFlag) was not recognized as a function in the child of a child. The "Shop" input uses it's own callback and successfully updates the state. useState is executed and the returned value is stored as the initial state. I create the UI with a loop, so I would like to have a single callback for the updating the inputs. Jan 1, 2023 · I am having a state called mediaRecorder which is empty initially. This results in shorter and simpler expressions when accessing chained properties when the possibility exists that a reference may be missing. Dec 14, 2020 · I'm working on a flashcard App, my flashcard component is as below: import React, { useState } from 'react'; import '. url Oct 2, 2015 · In my react component im trying to implement a simple spinner while an ajax request is in progress - im using state to store the loading status. 8. Don't use useState as you were using the setState function from classes. Some mocking libraries also don't deal with arrow functions particularly well (i. According to the tutorial doc, I this should refer to the component. queued up for the next render, so the log is displaying the state value from the current render cycle. Nov 19, 2019 · It's not React-specific: that's an async function, so the promise is going to resolve after the console log occurs, that's why you get undefined. The useState hook is a powerful addition to React, introduced in version 16. If you need to work with the state directly after it's been changed, do it in a useEffect with the state variable in the dependency array. Ensure react and react-dom are of the same version. div` background-image: url(${props. May 8, 2022 · React state is undefined when setting it with a hook. In this useState Hi, react noob here. log. Cannot read property of undefined react redux. log(self. : setSelectedUsers(undefined); Sep 9, 2019 · The only solution I have found is to set the state (even though I have no desire to change the state), and use the state-setting function as a workaround to reading the state, setting the "new" state to being the same as the previous state (setupConsoleCallback(() => {setCount(prevCount => {console. Am I missing something? Nov 29, 2017 · In this case, either use arrow function as: render() { createMenuItems = (items) => { console. products is undefined. It's a quirk/feature of the React ecosystem. if you do console. Jul 3, 2019 · You already have many states. I am having an issue where calling setState() using the useState() hook in one component is causing state to become undefined in another component. Aug 29, 2019 · Thanks for contributing an answer to Stack Overflow! Please be sure to answer the question. Given the context above, is there any problem with passing undefined to the React state? I. state in functions inside my component. So setMessage function will return undefined which will be your onClick callback. I am gonna use that data for convert money but I am getting this Jan 2, 2020 · Once React renders the HTML part then from onClick={setMessage('Boom')} will be evaluated in the same time. If you want to console. js file import ReactDOM react state is undefined inside the function. current const [state,setState] = useState(stateRef); async function some() { stateRef = { some: 'value' } setState(stateRef) // Triggers re-render await some2(); } async function some2() { await someHTTPFunctionCall(stateRef. data) probably won't print the correct results, as React will queue the setState call. React useState keep giving me undefined. JS which shows all the Images passed to it in an array and onMouseOver it shows a button below. --Solution, based on the May 1, 2021 · You cannot use a hook outside of the top level of a functional component or hook see docs As you are using class-based components, you should use setState method to update your state or switch to functional component and use useState hook I don't see any usage of searchTerm in your code, but I am assuming, that you will add a function to your or use arrow function: onSubmitEditing={(e) => this. state) // this is undefined console. I expected 'this' value may be Global variable Whenever I call function component . log(doSomething()), you will get logs like this. path and hence it's undefined. state) ); Jun 4, 2015 · I have a React component hierarchy like this: AgreementContentWidget AgreementTitleContainer AgreementTitle &lt;-- this is ok, but CommentList &lt;-- problem here SectionsConta May 27, 2022 · Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand Oct 20, 2019 · State is getting undefined inside the useCallBack hook I think it is not getting scope to the state variable const [selectedLocation, setSelectedLocation] = useState() const selectLocationHandler = May 23, 2024 · With this implementation, the event handler function is fired for each user input. You could instead give a function as argument to toggleFlag. Nov 21, 2021 · From the output, it’s apparent that this is the instance cat in the function call cat. Now let’s define an object dog in the same environment Apr 1, 2019 · The functional argument that you pass to setState is only really useful when you want to conditionally set the state by diffing the previous state (I mean you can just do it with logic surrounding the call to setState but I think it looks cleaner in the function) or if you set state in a closure that doesn't have immediate access to the I am making an application using React and redux. When I try and update the lightState using the setLightState function it returns undefined for the current state. some Mar 5, 2020 · As far as I can tell your hook has a flaw: after the initial render your event handler is not attached because the ref is undefined. I tested 'this' variable in React's Arrow function component. Here is the definition of the bind method Jan 28, 2024 · This means that by the time React processes state updates, it’s possible the code following await will run with outdated state. Oct 22, 2020 · Because you are already passing index in parent function this. Nov 29, 2020 · A novice at React over here, struggling with a basic useState hooks program. something);}); Mar 13, 2019 · You should read the React Component Life Cycle here. Easier though, would probably be too see if useIntersectionObserver takes a dependency array. Here, a => a + 1 is your updater function. React states remain undefined. Jan 15, 2021 · Also react state updates are asynchronous so when you're trying to console. yay //you called a functions its executed undefined // you called a function which will not return anything first log is from doSomething file1. May 22, 2020 · React state updates are asynchronous, i. If you meant to render a collection of children, use an array instead. What I am trying to do is using the data from redux action, and display those variable. const stateRef = React. log(userName) // correctly gives String console. Update Oct 18, 2021 · TypeError: Cannot read property ‘state’ of undefined. So, I am trying to use the data from the first API to retrieve the Data in the Few Things: *Stateless Functional Components don't have state, lifecycle methods, and this keyword. So, whenever we define a component in react, along with the n number of properties it has, say Aug 12, 2022 · What happened to this which was undefined? Well, arrow functions do not have this of their own! They refer to this of the lexical environment/context inside which they are declared. How to actually store functions Apr 16, 2014 · Right, I'm probably missing the obvious here but I am getting an 'Uncaught TypeError: undefined is not a function' I seems to be . My solution that didn't use typescript or the propTypes library was to wrap setCity and setFlag in new functions in the first child and then pass those new functions to the next child. Nov 23, 2015 · You're using React. This is my components code (CategoryProducts. It returns money rates based on 'USD'. log(city. state property is considered "undefined" 0. React hooks state is undefined when updating. You can also just console log the state outside the useEffect and you'll see it being updated. The function given to setTimeout will get the flag variable from the initial render, since flag is not mutated. Dec 18, 2024 · That is a best practice in react, try to compute and retrieve state in as much functional ways as possible, i. Then, during the next render, it will call them in the same order: a => a + 1 will receive 42 as the pending state and return 43 as the next state. react state is undefined inside the function. Expanding on that example above, let’s say we extracted the list into its own component: class Quiz extends React. score = 0;. We can say the speak() is bound to cat. This is a no-op, but it indicates a memory leak in your application. playOrPauseSong(this. 7th. Using a function also ensures the initial state value only gets computed once. See the linked question, but in short: You need to: 1. Try to do the assignment in the constructor() function or call this. If you're working with React class components, you may find yourself vexed by 'this. The state of the component turn out to be undefined and nothing display on view. second log is from file2. Feb 13, 2021 · I had a similar problem. state) on the next line and expect to see the state updated. Component with ES2015 class syntax you need to bind your action handlers to a context of your class. Feb 11, 2022 · In React class-based components when we use event handler callbacks, it is very important to give special attention to the 'this' keyword. This will render a page refresh, and then use the React Ref in the async function. I tried logging out the data and I found out that it runs twice because of the strict mode. import React, { useEffect, Feb 14, 2022 · every time I invoke onClick function it just returns undefined! Nevertheless, 'React Developer Tools' shows that indeed these states have values!! I am unable to change the state from onClick function because it is always undefined. setState is not a function. cart, { title, desc, price, image, }, console. change it to: const BackgroundImage = (props) => { console. Provide details and share your research! But avoid …. One way to solve this problem would be to use a variable: componentDidMount: function() { var self = this; setInterval(function() { console. _handleTextChange(e)} /> Edit. Jul 21, 2020 · When you define function in your component without using arrow function you have to bind to each function the this keyword in the constructor for that function to consider each reference of this in if definition to refer to the created component. gradeSelection in Subjects. And when using setstate, keep in mind that any objects defined int he state will be updates as a whole object Sep 18, 2020 · I have a functional component with hooks, and I'm trying to pass the update function to another component, but it's always undefined. useState, then this function is executed, when React. I've gone ahead a written up a summary of the code and then restated the issue more specifically afterwards. state has not been assigned to when groupByCategory is first called. The data is retrieved from the redux action and store as props. For some reason this piece of code below in my React Aug 3, 2017 · Using this construct: componentWillReceiveProps(nextProps) { this. Commented Feb 21, React: 'this. setState works! Binding this to the Mar 25, 2023 · When the other context reaches into the ref, it will always get the latest function back out. – germanfr. total + price })); } May 22, 2019 · React hooks introduces useState for setting component state. NOTE, if you executing the function (like function()) rather then just passing a reference (like function) you HAVE to use an arrow, or simple, function => since than it will be executed on load rather then onClick. , arrow functions aren't on the prototype, but on the instance). js: Year 12 // correct subjectCards. setState` instantly. After a particular process this state is updated to a new value. The caveat with instance property functions is that there's a function created per-component. companies every time the component receives ANY props, even when there are no companies in the props. state Aug 29, 2016 · When you extend React. It takes the pending state and calculates the next state from it. In general react and react-dom should always be the same version in package. Because so far as I know, 'this' in arrow function is I've got a few React functional Components that I would like to share a state. props. //main index. You can read eslint docs which states: A bind call or arrow function in a JSX prop will create a brand new function on every single render. Right now I'm blocked where I want a directional keypress to change the state of the Mar 18, 2022 · My problem is the next: I want to encapsulate a functional component out of the App main component, the problem is that having the State its own values, in the functional component, which calls a custom hook, is undefined. state property is considered "undefined" 4. So calling it results in undefined . users. users) // this is the error // and so this code doesn't work /*this. Aug 14, 2018 · The problem could be that you wouldn't have initialised state in the constructor and since this. js Apr 29, 2022 · State Remains Undefined in React. Hot Network Questions Nov 22, 2016 · I have a scenario where I'm passing data from a reducer into my react state. I cannot understand why is this happening, taking into account that state is being invoked with useState hook. If you want to print your state after a call to setState you have to supply a callback: this. I am getting data from API and I will use the data. Mar 2, 2018 · I am new at React and trying to learn it. If it does, then any state you utilize in fetchMore should be sent to the dependency array of that hook. Now if binding all Oct 18, 2021 · TypeError: Cannot read property ‘ state ’ of undefined. Let’s look back at some code from Element. This is because setState is asynchronous. Try this: onChange={e => _handleTextChange(e)} I tried using the && and made the state null, the problem now is that React is saying "Error: Objects are not valid as a React child (found: object with keys {name}). here is the code : The Oct 14, 2014 · In your first example, this is out of scope when the callback function fires. e. dev Feb 11, 2022 · useState Hook is used to access state in the React functional components. log(`Count is: ${prevCount}`); return May 5, 2022 · Setting state is neither sync nor async. It could log out the state value with two added values instead of one, but it immediately changed to undefined. this. My problem is that my variable is undefined after a filter function executed. Function overloading / dynamic Sep 13, 2017 · songBuilder()--returns "undefined" since this points to the window. This function will get the correct flag value as argument, and what is returned from this function is what will replace I'm trying to store product from an API in the state of my React component and then map them in the render function of the component but somehow this. useEffect(()=>{ initializeContext(); }, []) Not in function component. js : class Element extends Component { constructor ( props ) { super ( props ) ; this . Apr 29, 2022 · React state is undefined when setting it with a hook. setState is asynchronous the state may not be initialsed before you are trying to access in changeCbState function. What is this used for in a class? So, whenever we define a component in react, along with the n number of properties it has, say, Jan 27, 2022 · I am having an issue where calling setState() using the useState() hook in one component is causing state to become undefined in another component. Feb 7, 2022 · I am trying to retrieve data from an API, however it requires an encrypted name, which I receive from another API call. setState() inside componentDidMount() which will call the render() function again. map() that's the problem but I can not see why. render() { { this. So instead you could update to following. Is there something I might possibly be doing wrong? Console output: App. Oct 11, 2022 · Playing around with react-redux and my state isCartVisible is showing undefined, I used simple functional components and I'm storing my stores in different files. It can be handy to always have this in your render function when developing: console. Sep 1, 2017 · ES6 Function binding gets undefined (this. Uncaught TypeError: this. Jan 15, 2022 · this. var idealist = React. state); so you can watch all updates and also see if you need to optimize to reduce re-renders with a shouldComponentUpdate function. At that point, Product will be whatever you set as the default. state undefined in React component render function. state' is undefined inside a component function. ". You can add a second useEffect with the state as a dependency and just console log it there. render => {} do. In these cases the context this is undefined when the callback function actually gets invoked that's why we have to bind the context of this. Make the code pretty! In react there are 2 types of components. This is a pretty common footgun with React. log when the state has been updated then you could use another useEffect with city in the dependency array. In this event function, we have a setUser() state function that accepts the previous/current state of the user and unpacks this user state using the spread operator. state captures the values) 0. Jun 5, 2020 · I have a simple React Hooks component. You should use external state like Redux or Flux or something else for May 12, 2021 · My code is straight forward and it looks like I am using list as the local state and have updated it once data are fetched, the list is perfectly loading on the tbody but still is undefined inside Jul 3, 2017 · You should use the second form of setState that accepts a callback function which receives previousState and previousProps as an argument. Ensure that you have also updated the react-dom package and it is of the same version as react. I'm getting undefined for this, and therefore cannot read property 'setState' attempting to set state within the return of a function that Feb 21, 2020 · Otherwise, this will be undefined when that function is called. setState({ companies: nextProps. json as the React team updates them together. Component { Apr 24, 2021 · If you add a function via addEventListener the state it accesses is captured in the closure, meaning your function will always see the state as it was at the time of binding. state = { value : 1 } ; } Feb 4, 2015 · You can "persist" the state using local storage as Omar Suggest, but it should be done once the state has been set. addTotal(price) { this. This is important if determining your initial state requires an expensive computation - if you pass it directly, then the value will be computed every time the component renders, compared Sep 30, 2021 · To understand why it will be undefined, you need to know two things about state update in React: It is updated asynchronously; It is constant within a particular render of a component. Mar 8, 2019 · I've two componentes: Orders and FormDialog, the first is father of the second. searchMode. A simple functional component created named CounterHooks that aims at making a simple +-1 counter. My function looks like this addToCart({ title, desc, price, image }) { // This is what is returning undefined this. setState((prevState, previousProps) => ({ counter: prevState. state); }, 3000); } Jun 7, 2022 · remove initializeContext() from function ,You should call this in useEffect. An advice, If you don't wanna get confused and work with useState like you were using the setState from classes, use the same "labels" for the variable and try, if you can, to have one state. concat(userName) })*/ } I want to update loopActive state on toggle, but this object is undefined in the handler. I planed on using setState to check the variable hover if is Apr 16, 2021 · So you can execute it on the spot without any new function onClick={() => addRemoveFav(show)}. Mar 29, 2022 · react state is undefined inside the function. render: function {} or switch to ES6 classes, which would make your current class look like this Mar 14, 2018 · you have a scope issue. For that you need to pass a callback to the setState function and you need to serialize and deserialize the objects put into local storage. This is just normal JS behaviour -- the value is undefined at the point console. Only if some other state changes that trigger a re-render will more or less accidentally also cause the useEffect to re-evaluate and eventually attach the event Jul 29, 2017 · React: undefined the state of `this. Component class. BTW like mentioned by other users, when starting off with React it would be a lot easier to get going with function components, rather than jumping right into Class onesThe learning curve would be much less steeper Sep 5, 2022 · I think, data is contains value = undefined so you should check if it data contains some value other than so called falsy values, such as (NULL, undefined) You can do this Jun 8, 2019 · The reason it's undefined it's that your firstSong was still undergoing network request which is async method, and hence there wont be any firstSong nor firstSong. js): Apr 19, 2023 · I created the reducer function and whenever I try to append an array within the nested object it makes the whole state undefined. Asking for help, clarification, or responding to other answers. This is okay if there aren't many of them on the page, but it's something to keep in mind. I. main) right after you setCity there is no guarantee that the state has been updated. Component, also a few other obvious fixes. But when the value of this state is called in the useEffect it is returning the initial empty value: const [mediaRecorder, setMediaRecorder] = useState(); When the other context reaches into the ref, it will always get the latest function back out. createClass with arrow functions, this messes up the binding to this. However it appears as undefined once before loading the new values. I don't know the size of your project but I personally advise against using the current state of the component to manipulate datas. setState((state) => ({ cart: [ this. 2. cart) ], })); } and my items Oct 26, 2017 · You should set the state inside the request callback. log(this. – May 6, 2020 · You are missing 'state' in your console. map is not a function. js: Year 12 // correct Subject. Mar 31, 2021 · The function won't be called until React is actually ready to setup the state. What is this used for in a class?. Oct 3, 2021 · I declared a state named product with initial values. Aug 20, 2021 · By passing a function to setState, the new state is computed using the previous value on the queue and not the initial one. I have one container - ChatApp - and one component UserInput. props, this. The trick is to remove and re-add the listener when your state changes, then it will see the correct state and update the state correctly. Apr 10, 2019 · Important to note: If you provide a function in React. React state is undefined when setting it with a hook. Not able to access react State inside a function. 13. . I have a UI with multiple inputs with values in an object. React State Nov 12, 2019 · To get stuck in with react hooks I decided to try and make snake and use useReducer/useContext state management. Also, setting state in React is asynchronous, so you can't setState() then console. I've trying to send data as properties from Orders to FormDialog as follows: Orders Component class Orders extends Jan 9, 2023 · With this method you can easily call this function in the componentDidMount and wait the data before render your html in your render function. writing functions that have a clear in and output and expose the necessary API from the return of the given function. Apparently arrow functions inside render is also a bad practice (Thx to Adam Terlson in the comments and answer below). But the "Product" inputs never update the state. Component can't see the updated state until it re-renders; In light of the above two points, we cannot use questions in the third then() method's callback function. *You need to connect General and Application component so that Application component can you the state value of General component. Looks like @trekforever found your problem. As as aside, your console. This causes problems when I want to map its value. In this example two toggle buttons that would conditionally show/hide a searchbar and a navbar. : Type 'null' is not assignable to type 'string[] | undefined'. React state variable value appearing to be null. js: undefined // not correct App. For some reason in searchItems, this. But how can I use hooks to replace the callback like below code: setState( { name: "Michael" }, () => console. setState({something: 'blah'}, function() { console. In our case, the function updateCounter is defined inside the class App, and it refers to the this of the class, hence, this. Sep 17, 2018 · The problem is you are calling the functions which will not return anything. aieuqf ywtiwagg mcdfnw qljj woeou havcjt jzacbdst xbdgdz cxuplyl numhgm