How to toggle boolean state of react component?

Question

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

I have a 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?

Answer 1

Since nobody posted this, I am posting the correct answer. If your new state update depends on the previous state, always use the functional form of setState which accepts as argument a function that returns a new state.

In your case:

this.setState(prevState => ({   check: !prevState.check })); 

See docs

---

Since this answer is becoming popular, adding the approach that should be used for React Hooks (v16.8+):

If you are using the useState hook, then use the following code (in case your new state depends on the previous state):

const [check, setCheck] = useState(false); // ... setCheck(prevCheck => !prevCheck); 

Answer 2

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.

Upd: As pointed out in comments this approach might lead to unexpected results since React's state is asynchronous. The correct way in this case will be to use callback:

this.setState(({ check }) => ({ check: !check }));