Reactjs state not updating

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  constructor(props) {

    super(props);
    this.state = {
      active: false,
      showSideBar: false,
      className: ""
    }
  }
  componentDidMount() {
    if (this.props.overlay) {
      this.setState({
        className: "wrapper_overlay"
      });
      alert(this.state.className);
    }
    else if (this.props.SideBarWithIcon) {
      this.setState({
        className: "wrapper_clopsed"
      });
    }
  }

I am updating my state with the help of the props but the component is getting props but state is not updating

setState is asynchronous. Just alert in a callback to the method instead.

if (this.props.overlay) {
  this.setState(
    { className: "wrapper_overlay" },
    () => alert(this.state.className);
  );
}

Note: you can, and should, also use shouldComponentUpdate to check for when a setState call completes

(React) setState not updating - JavaScript, Hi friends, setState is not updating values in the state for some reason when I pause the timer although it's receiving correct parameters. For some reason, it is not updating the state. I put a console log in the 'if' part of my use effect to check it was even getting to that bit and the console log prints out fine so I am not sure as to why the button will not change.

Since setstate is async in nature so you maynot see updated state in alert. You can use that in callback which will be called once the setstate is done. like this

componentDidMount() {
    if (this.props.overlay) {
      this.setState({
        className: "wrapper_overlay"
      }, ()=> {alert(this.state.className);});
   }

React setState usage and gotchas, apply the new values to the state until the component is reconciled. reactjs - React Child Component Not Updating After Parent State Change - Stack Overflow. I'm attempting to make a nice ApiWrapper component to populate data in various child components. From everything I've read, this should work: https://jsfiddle.net/vinniejames/m1mesp6z/1/class. Stack Overflow.

State updates may be asynchronous

React may batch multiple setState() calls into a single update for performance.

Because this.props and this.state may be updated asynchronously, you should not rely on their values for calculating the next state.

// Wrong
this.setState({
    className: "wrapper_overlay"
  });

To fix it, use a second form of setState() that accepts a function rather than an object.

// Correct
this.setState((state, props) => ({
  className: "wrapper_overlay"
}));

or just

this.setState(() => ({
  className: "wrapper_overlay"
}));

Why my setState doesn't work?, Can't perform a React state update on an unmounted component This is a no op? This happens because ItemList is pure, and because pushing a new item on the this.state.items array does not replace the underlying array. When ItemList is asked to re-render, it will notice that its props haven’t changed and it will not re-render. Recap. So there you go: that’s why you shouldn’t mutate state, even if you immediately call setState.

In React.js, running program thread does not wait for setting state and continues its execution, until and unless operation defined in setState() callback.

Your state is getting set but as your alert() is after setstate i.e. not in callback of setState() that's why its getting previous value because at the time state is setting new value, thread is not waiting but executing the next instruction which is alert().

if (this.props.overlay) {
    this.setState({ className: "wrapper_overlay" }, () => alert(this.state.className););
}

Hope this works for you.

React state update on an unmounted component, , but it indicates a memory leak in your application. To fix, cancel all subscriptions and asynchronous tasks in a useEffect cleanup function. From React's documentation: setState () does not immediately mutate this.state but creates a pending state transition. Accessing this.state after calling this method can potentially return the existing value. There is no guarantee of synchronous operation of calls to setState and calls may be batched for performance gains.

Just use the callback method to update the state, as setState() might work asynchronously.

        this.setState(() => {
            className: "wrapper_clopsed"
        });

React Lifecycle Methods- how and when to use them, React JS - setState doesn't update the state immediately. setState is asynchronous. It means you can't call setState on one line and assume state has changed on the next. setState() does not immediately mutate this. // This is because `incrementCount()` function above reads from `this.state.count`, // but React doesn't update `this.state.count` until the component is re-rendered. // So `incrementCount()` ends up reading `this.state.count` as 0 every time, and sets it to 1. // The fix is described below!}

React JS - setState doesn't update the state immediately, state may be updated asynchronously, you should not rely on their values for calculating the next state. State updates in React are not applied  React may batch multiple setState() calls into a single update for performance. Because this.props and this.state may be updated asynchronously, you should not rely on their values for calculating the next state. For example, this code may fail to update the counter:

Why React setState/useState does not update immediately, React setState and useState are asynchronous actions. React setState and useState only create queues for React core to update the state of React components. State variables can hold objects and arrays just fine, so you can still group related data together. However, unlike this.setState in a class, updating a state variable always replaces it instead of merging it. We provide more recommendations on splitting independent state variables in the FAQ. Next Steps

Component State – React, setState() schedules an update to a component's state object. When state changes, the Example of code that will not behave as expected: incrementCount()  So long as you modify the state by clicking the hamburger then it animates properly. If you modify the state outside of the hamburger component the hamburger does not animate. I got a workaround to work by creating a ref to the hamburger and then calling the ._animate() function manually whenever I update the state:

Comments
  • You can ditch the constructor and directly write state = {}. For more info: hackernoon.com/…