[javascript] How to toggle boolean state of react component?

I'd like to know how to toggle a boolean state of a react component. For instance:

I have boolean state check in the constructor of my component:

constructor(props, context) { 
   super(props, context);

   this.state = {
      check: false
   };
};

I am trying to toggle the state each time my checkbox is clicked, using the this.setState method:

<label><input type=checkbox" value="check" onChange = {(e) => this.setState({check: !check.value})}/> Checkbox </label>

Of course I get a Uncaught ReferenceError: check is not defined. So how can I achieve this?

Many thanks in advance.

Use checked to get the value. During onChange, checked will be true and it will be a type of boolean.

Hope this helps!

class A extends React.Component {_x000D_
  constructor() {_x000D_
    super()_x000D_
    this.handleCheckBox = this.handleCheckBox.bind(this)_x000D_
    this.state = {_x000D_
      checked: false_x000D_
    }_x000D_
  }_x000D_
  _x000D_
  handleCheckBox(e) {_x000D_
    this.setState({_x000D_
      checked: e.target.checked_x000D_
    })_x000D_
  }_x000D_
  _x000D_
  render(){_x000D_
    return <input type="checkbox" onChange={this.handleCheckBox} checked={this.state.checked} />_x000D_
  }_x000D_
}_x000D_
_x000D_
ReactDOM.render(<A/>, document.getElementById('app'))

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>_x000D_
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>_x000D_
<div id="app"></div>

Set: const [state, setState] = useState(1);

Toggle: setState(state*-1);

Use: state > 0 ? 'on' : 'off';

Depending on your context; this will allow you to update state given the mouseEnter function. Either way, by setting a state value to either true:false you can update that state value given any function by setting it to the opposing value with !this.state.variable

state = {
  hover: false
}

onMouseEnter = () => {
  this.setState({
    hover: !this.state.hover
  });
};

You should use this.state.check instead of check.value here:

this.setState({check: !this.state.check})

But anyway it is bad practice to do it this way. Much better to move it to separate method and don't write callbacks directly in markup.

You could also use React's useState hook to declare local state for a function component. The initial state of the variable toggled has been passed as an argument to the method .useState.

import { render } from 'react-dom';
import React from "react";

type Props = {
  text: string,
  onClick(event: React.MouseEvent<HTMLButtonElement>): void,
};

export function HelloWorldButton(props: Props) {
  const [toggled, setToggled] = React.useState(false); // returns a stateful value, and a function to update it
  return <button
  onClick={(event) => {
    setToggled(!toggled);
    props.onClick(event);
  }}
  >{props.text} (toggled: {toggled.toString()})</button>;
}


render(<HelloWorldButton text='Hello World' onClick={() => console.log('clicked!')} />, document.getElementById('root'));

https://stackblitz.com/edit/react-ts-qga3vc

Here's an example using hooks (requires React >= 16.8.0)

// import React, { useState } from 'react';_x000D_
const { useState } = React;_x000D_
_x000D_
function App() {_x000D_
  const [checked, setChecked] = useState(false);_x000D_
  const toggleChecked = () => setChecked(value => !value);_x000D_
  return (_x000D_
    <input_x000D_
      type="checkbox"_x000D_
      checked={checked}_x000D_
      onChange={toggleChecked}_x000D_
    />_x000D_
  );_x000D_
}_x000D_
_x000D_
const rootElement = document.getElementById("root");_x000D_
ReactDOM.render(<App />, rootElement);

<script crossorigin src="https://unpkg.com/react@16/umd/react.development.js"></script>_x000D_
<script crossorigin src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script>_x000D_
_x000D_
<div id="root"><div>

I was landed in this page when I am searching to use toggle state in React component using Redux but I don't find here any approach using the same.

So, I think it might help someone who was struggling to implement toggle state using Redux.

My reducer file goes here. I get the initial state false by default.

const INITIAL_STATE = { popup: false };
export default (state = INITIAL_STATE, action) => {
    switch (action.type) {
        case "POPUP":
            return {
                ...state,
                popup: action.value
            };
        default:
            return state;
    }
    return state;
};

I change state on clicking the image. So, my img tag goes here with onClick function.

<img onClick={togglePopup} src={props.currentUser.image} className="avatar-image avatar-image--icon" />

My Toggle Popup function goes below, which call Dispatcher.

const togglePopup = ev => {
    ev.preventDefault();
    props.handlePopup(!props.popup);
};

This call goes to below mapDispatchToProps function which reflects back the toggled state.

const mapDispatchToProps = dispatch => ({
    handlePopup: value => dispatch({ type: "POPUP", value })
});

Thank you.

Try:

<label><input type=checkbox" value="check" onChange = {(e) => this.setState({check: !this.state.check.value})}/> Checkbox </label>

Using check: !check.value means it is looking for the check object, which you haven't declared.

You need to specify that you want the opposite value of this.state.check.

I found this the most simple when toggling boolean values. Simply put if the value is already true then it sets it to false and vice versa. Beware of undefined errors, make sure your property was defined before executing

this.setState({
   propertyName: this.propertyName = !this.propertyName
});