React - Uncaught Typeerror: Cannot Read Property 'Setstate' of Undefined

React - uncaught TypeError: Cannot read property 'setState' of undefined

This is due to this.delta not being bound to this.

In order to bind set this.delta = this.delta.bind(this) in the constructor:

constructor(props) {
    super(props);

    this.state = {
        count : 1
    };

    this.delta = this.delta.bind(this);
}

Currently, you are calling bind. But bind returns a bound function. You need to set the function to its bound value.

TypeError: Cannot read properties of undefined (reading 'setState')

If you declare your function in the following manner

    setEmailVal = val => {
        this.setState({email: val.currentTarget.value});
    }

It works fine.

If you wish to do it in the other (old, if I am not wrong) way, then you'd need to bind the function to the class for the subcomponent, i.e. the onChange handler in the class to "see" it:

    constructor(props) {
        super(props);
        this.state = {email: ""};
        this.setEmailVal = this.setEmailVal.bind(this);
    }

Lastly, you could do a direct bind inside the return component itself

        return (
            <input type="text" onChange={this.setEmailVal.bind(this)} value={this.state.email} />
        );

React - TypeError: Cannot read property 'setState' of undefined

You need to bind updateTime

constructor(props) {
   ...
   this.updateTime = this.updateTime.bind(this)
}

or use arrow function

updateTime = () => {
    //updating the time by set state
    this.setState( (state,props) =>  {date:new Date()}  );
}

and change your setState to

this.setState({
  date: new Date()
});

or

this.setState( (state,props) =>  ({date:new Date()})  );

TypeError: Cannot read property 'setState' of undefined react

   navigator.geolocation.getCurrentPosition(function (position) {
      this.setState({
        lat: position.coords.latitude,
        lng: position.coords.longitude,
      });
    });

React doesn't understand this in here because its referring to the function scope, not React scope. You can change the syntax to fat arrow function, which using lexical scoping/this

navigator.geolocation.getCurrentPosition( (position) => {
      this.setState({
        lat: position.coords.latitude,
        lng: position.coords.longitude,
      });
    });

How to fix Cannot read property 'setState' of undefined in React

You lost context here since anon. function used:

    ref.once("value").then(function onSuccess(res) {
        console.log("success", res.val())

        this.setState({db: res.val(), loading: false})
        // ERROR GOES HERE 'Unhandled Rejection (TypeError): Cannot read property 'setState' of undefined'

    });

Use arrow function lilke this:

ref.once("value").then((res) => {
    console.log("success", res.val())

    this.setState({db: res.val(), loading: false})
    // ERROR GOES HERE 'Unhandled Rejection (TypeError): Cannot read property 'setState' of undefined'

});

React Cannot read property 'setState' of undefined in if-block

In your getFilteredTrades and getAllTrades functions this refers to the functions itself and not the object and those functions don't have a member setState.

You can resolve the problem in two ways:

1. Declaring them as arrow functions which does not bind this by writing getFilteredTrades = () => { ... } and getAllTrades = () => { ... }.
2. Bind the this keyword of the functions to the class object by writing this.getFilteredTrades = this.getFilteredTrades.bind(this) and this.getAllTrades = this.getAllTrades.bind(this) in your constructor.

Cannot read property 'setState' of undefined in ReactJs

Try initializing your state inside a constructor and bind the function like below

constructor(props) {
        super(props);

        this.state = {
            alpha: ""
        };

        this.handleChange = this.handleChange.bind(this);
    }

    handleChange(e) {
        this.setState({
            alpha: e.target.value
        });
    }

React JS: Cannot read property 'setState' of undefined when updating from React.createClass

your this in onChange is undefined, which is caused by not binding.

add these:

constructor(props) {
  super(props);
  this.onChange = this.onChange.bind(this);
}

FYI,

• https://facebook.github.io/react/docs/handling-events.html
• React this is undefined

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