243

I am writing a simple component in ES6 (with BabelJS), and functions this.setState is not working.

Typical errors include something like

Cannot read property 'setState' of undefined

or

this.setState is not a function

Do you know why? Here is the code:

import React from 'react'

class SomeClass extends React.Component {
  constructor(props) {
    super(props)
    this.state = {inputContent: 'startValue'}
  }

  sendContent(e) {
    console.log('sending input content '+React.findDOMNode(React.refs.someref).value)
  }

  changeContent(e) {
    this.setState({inputContent: e.target.value})
  } 

  render() {
    return (
      <div>
        <h4>The input form is here:</h4>
        Title: 
        <input type="text" ref="someref" value={this.inputContent} 
          onChange={this.changeContent} /> 
        <button onClick={this.sendContent}>Submit</button>
      </div>
    )
  }
}

export default SomeClass
5
  • It's not the problem here, but you should avoid refs.
    – Brigand
    Commented Apr 11, 2015 at 13:12
  • @FakeRainBrigand how would you solve it without refs here? Commented Apr 11, 2015 at 13:51
  • 3
    Well in your current code, just change React.findDOMNode(React.refs.someref).value) to this.state.inputContent and delete ref="someref".
    – Brigand
    Commented Apr 12, 2015 at 8:21
  • You don't need refs since you're updating the value inside state. Just send the state value. Commented Apr 27, 2016 at 18:00
  • Your function needs binding in ES5 inorder to access state or props inside a function but if you use arrow function then you no need to do manual binding the binding takes automatically and you can also stay away from scope related issues Commented Aug 27, 2018 at 5:58

19 Answers 19

270

this.changeContent needs to be bound to the component instance via this.changeContent.bind(this) before being passed as the onChange prop, otherwise the this variable in the body of the function will not refer to the component instance but to window. See Function::bind.

When using React.createClass instead of ES6 classes, every non-lifecycle method defined on a component is automatically bound to the component instance. See Autobinding.

Be aware that binding a function creates a new function. You can either bind it directly in render, which means a new function will be created every time the component renders, or bind it in your constructor, which will only fire once.

constructor() {
  this.changeContent = this.changeContent.bind(this);
}

vs

render() {
  return <input onChange={this.changeContent.bind(this)} />;
}

Refs are set on the component instance and not on React.refs: you need to change React.refs.someref to this.refs.someref. You'll also need to bind the sendContent method to the component instance so that this refers to it.

6
  • 6
    Nice thing on binding function in the constructor itself to prevent functions created multiple times Commented Sep 3, 2015 at 12:53
  • 1
    excuse me but I don't understand why this.changeContent needs to be bound to the component instance via this.changeContent.bind(this). I mean, we write a component through a subclass or React.Component and in ES6 every method defined in a class is automatically bound to the instance created through the subclass/class itself. Why here we need to do it "manually"? Is it something particular concerning React? Or am I worng about the dynamic of ES6 class methods?
    – marco
    Commented Dec 26, 2016 at 23:33
  • 9
    In ES6, methods defined on a class are not automatically bound to the instance. Which is why, when you need to, you need to manually bind them. With BabelJS, using the property initializer syntax and arrow functions, you can directly define methods that will be automatically bound to the instance. myMethod = () => ... instead of myMethod() { ... }. Commented Dec 27, 2016 at 11:20
  • 1
    @AlexandreKirszenberg take a look at this example: the method seems to be automatically bound to the instance...
    – marco
    Commented Dec 27, 2016 at 20:58
  • 2
    @marco Here's a different example. When you call a method with object.method(), the this variable inside the body of method will refer to object. But if you pass object.method to another function, only the value of the function itself will be passed, and it will lose the object context. Which is why, with React, you sometimes need to manually bind an event handler before passing it to a component, so as not to lose the context of the current component instance. Commented Dec 28, 2016 at 9:47
105

Morhaus is correct, but this can be solved without bind.

You can use an arrow function together with the class properties proposal:

class SomeClass extends React.Component {
  changeContent = (e) => {
    this.setState({inputContent: e.target.value})
  } 

  render() {
    return <input type="text" onChange={this.changeContent} />;
  }
}

Because the arrow function is declared in the scope of the constructor, and because arrow functions maintain this from their declaring scope, it all works. The downside here is that these wont be functions on the prototype, they will all be recreated with each component. However, this isn't much of a downside since bind results in the same thing.

6
  • 1
    This works perfectly in TypeScript too (usually don't have to worry about binding in TypeScript, but I guess this is different)
    – mejdev
    Commented Feb 22, 2016 at 19:17
  • This doesn't work. I get 'property declarations can only be used in a .ts file'
    – BHouwens
    Commented May 5, 2016 at 15:48
  • @BHouwens Here it is in the babel REPL. I don't know what you are doing, but you are doing something wrong.
    – Kyeotic
    Commented May 5, 2016 at 20:24
  • It could be that I've set a constructor, but other than that my example is the same and doesn't compile. The bind method works though.
    – BHouwens
    Commented May 6, 2016 at 7:02
  • 3
    A constructor will not break this code, you must have another issue. Perhaps you don't have the correct plugin? This isn' part of the 2015 preset, it's called babel-plugin-transform-class-properties. If you show me your code I can tell you what the issue is. The babel repl gives you a nicely shareble link.
    – Kyeotic
    Commented May 6, 2016 at 16:00
57
+50

This issue is one of the first things most of us experience, when transitioning from the React.createClass() component definition syntax to the ES6 class way of extending React.Component.

It is caused by the this context differences in React.createClass() vs extends React.Component.

Using React.createClass() will automatically bind this context (values) correctly, but that is not the case when using ES6 classes. When doing it the ES6 way (by extending React.Component) the this context is null by default. Properties of the class do not automatically bind to the React class (component) instance.


Approaches to Solve this Issue

I know a total of 4 general approaches.

  1. Bind your functions in the class constructor. Considered by many as a best-practice approach that avoids touching JSX at all and doesn't create a new function on each component re-render.

    class SomeClass extends React.Component {
      constructor(props) {
        super(props);
        this.handleClick = this.handleClick.bind(this);
      }
      handleClick() {
        console.log(this); // the React Component instance
      }
      render() {
        return (
          <button onClick={this.handleClick}></button>
        );
      }
    }
    
  2. Bind your functions inline. You can still find this approach used here and there in some tutorials / articles / etc, so it's important you're aware of it. It it the same concept like #1, but be aware that binding a function creates a new function per each re-render.

    class SomeClass extends React.Component {
      handleClick() {
        console.log(this); // the React Component instance
      }
      render() {
        return (
          <button onClick={this.handleClick.bind(this)}></button>
        );
      }
    }
    
  3. Use a fat arrow function. Until arrow functions, every new function defined its own this value. However, the arrow function does not create its own this context, so this has the original meaning from the React component instance. Therefore, we can:

    class SomeClass extends React.Component {
      handleClick() {
        console.log(this); // the React Component instance
      }
      render() {
        return (
          <button onClick={ () => this.handleClick() }></button>
        );
      }
    }
    

    or

    class SomeClass extends React.Component {
      handleClick = () => {
        console.log(this); // the React Component instance
      }
      render() {
        return (
          <button onClick={this.handleClick}></button>
        );
      }
    }
    
  4. Use utility function library to automatically bind your functions. There are a few utility libraries out there, that automatically does the job for you. Here are some of the popular, just to mention a few:

    • Autobind Decorator is an NPM package which binds methods of a class to the correct instance of this, even when the methods are detached. The package uses @autobind before methods to bind this to the correct reference to the component's context.

      import autobind from 'autobind-decorator';
      
      class SomeClass extends React.Component {
        @autobind
        handleClick() {
          console.log(this); // the React Component instance
        }
        render() {
          return (
            <button onClick={this.handleClick}></button>
          );
        }
      }
      

      Autobind Decorator is smart enough to let us bind all methods inside a component class at once, just like approach #1.

    • Class Autobind is another NPM package that is widely used to solve this binding issue. Unlike Autobind Decorator, it does not use of the decorator pattern, but really just uses a function inside your constructor that automatically binds the Component's methods to the correct reference of this.

      import autobind from 'class-autobind';
      
      class SomeClass extends React.Component {
        constructor() {
          autobind(this);
          // or if you want to bind only only select functions:
          // autobind(this, 'handleClick');
        }
        handleClick() {
          console.log(this); // the React Component instance
        }
        render() {
          return (
            <button onClick={this.handleClick}></button>
          );
        }
      }
      

      PS: Other very similar library is React Autobind.


Recommendation

If I were you, I would stick with approach #1. However, as soon as you get a ton of binds in your class constructor, I would recommend you to explore one of the helper libraries mentioned in approach #4.


Other

It's not related to the issue you have, but you shouldn't overuse refs.

Your first inclination may be to use refs to "make things happen" in your app. If this is the case, take a moment and think more critically about where state should be owned in the component hierarchy.

For similar purposes, just like the one you need, using a controlled component is the preferred way. I suggest you to consider using your Component state. So, you can simply access the value like this: this.state.inputContent.

4
  • 5
    This is much more complete and useful than the accepted answer.
    – cortexlock
    Commented Feb 16, 2017 at 10:38
  • This is missing the method from this other answer stackoverflow.com/a/34050078/788260
    – Kyeotic
    Commented Aug 23, 2017 at 1:55
  • @Tyrsius , it's there. See approach #3 in my answer, a fat arrow function + the class properties proposal. Commented Aug 23, 2017 at 9:46
  • @KaloyanKosev what if not click action and just simple method call ? Commented Jun 26, 2018 at 12:59
9

Although the previous answers have provided the basic overview of solutions (i.e. binding, arrow functions, decorators that do this for you), I've yet to come across an answer which actually explains why this is necessary—which in my opinion is the root of confusion, and leads to unnecessary steps such as needless rebinding and blindly following what others do.

this is dynamic

To understand this specific situation, a brief introduction to how this works. The key thing here is that this is a runtime binding and depends on the current execution context. Hence why it's commonly referred to as "context"—giving information on the current execution context, and why you need to bind is because you loose "context". But let me illustrate the issue with a snippet:

const foobar = {
  bar: function () {
    return this.foo;
  },
  foo: 3,
};
console.log(foobar.bar()); // 3, all is good!

In this example, we get 3, as expected. But take this example:

const barFunc = foobar.bar;
console.log(barFunc()); // Uh oh, undefined!

It may be unexpected to find that it logs undefined—where did the 3 go? The answer lies in "context", or how you execute a function. Compare how we call the functions:

// Example 1
foobar.bar();
// Example 2
const barFunc = foobar.bar;
barFunc();

Notice the difference. In the first example, we are specifying exactly where the bar method1 is located—on the foobar object:

foobar.bar();
^^^^^^

But in the second, we store the method into a new variable, and use that variable to call the method, without explicitly stating where the method actually exists, thus losing context:

barFunc(); // Which object is this function coming from?

And therein lies the problem, when you store a method in a variable, the original information about where that method is located (the context in which the method is being executed), is lost. Without this information, at runtime, there is no way for the JavaScript interpreter to bind the correct this—without specific context, this does not work as expected2.

Relating to React

Here's an example of a React component (shortened for brevity) suffering from the this problem:

handleClick() {
  this.setState(({ clicks }) => ({ // setState is async, use callback to access previous state
    clicks: clicks + 1, // increase by 1
  }));
}

render() {
  return (
    <button onClick={this.handleClick}>{this.state.clicks}</button>
  );
}

But why, and how does the previous section relate to this? This is because they suffer from an abstraction of the same problem. If you take a look how React handles event handlers:

// Edited to fit answer, React performs other checks internally
// props is the current React component's props, registrationName is the name of the event handle prop, i.e "onClick"
let listener = props[registrationName];
// Later, listener is called

So, when you do onClick={this.handleClick}, the method this.handleClick is eventually assigned to the variable listener3. But now you see the problem arise—since we've assigned this.handleClick to listener, we no longer specify exactly where handleClick is coming from! From React's point of view, listener is just some function, not attached to any object (or in this case, React component instance). We have lost context and thus the interpreter cannot infer a this value to use inside handleClick.

Why binding works

You might be wondering, if the interpreter decides the this value at runtime, why can I bind the handler so that it does work? This is because you can use Function#bind to guarantee the this value at runtime. This is done by setting an internal this binding property on a function, allowing it to not infer this:

this.handleClick = this.handleClick.bind(this);

When this line is executed, presumably in the constructor, the current this is captured (the React component instance) and set as an internal this binding of a entirely new function, returned from Function#bind. This makes sure that when this is being calculated at runtime, the interpreter will not try to infer anything, but use the provided this value you given it.

Why arrow function properties work

Arrow function class properties currently work through Babel based on the transpilation:

handleClick = () => { /* Can use this just fine here */ }

Becomes:

constructor() {
  super();
  this.handleClick = () => {}
}

And this works due to the fact arrow functions do not bind their own this, but take the this of their enclosing scope. In this case, the constructor's this, which points to the React component instance—thus giving you the correct this.4


1 I use "method" to refer to a function that is supposed to be bound to an object, and "function" for those not.

2 In the second snippet, undefined is logged instead of 3 because this defaults to the global execution context (window when not in strict mode, or else undefined) when it cannot be determined via specific context. And in the example window.foo does not exist thus yielding undefined.

3 If you go down the rabbit hole of how events in the event queue are executed, invokeGuardedCallback is called on the listener.

4 It's actually a lot more complicated. React internally tries to use Function#apply on listeners for its own use, but this does not work arrow functions as they simply do not bind this. That means, when this inside the arrow function is actually evaluated, the this is resolved up each lexical environment of each execution context of the current code of the module. The execution context which finally resolves to have a this binding is the constructor, which has a this pointing to the current React component instance, allowing it to work.

2

You can tackle this by three ways

1.Bind the event function in the constructor itself as follows

import React from 'react'

class SomeClass extends React.Component {
  constructor(props) {
    super(props)
    this.state = {inputContent: 'startValue'}
    this.changeContent = this.changeContent.bind(this);
  }

  sendContent(e) {
    console.log('sending input content '+React.findDOMNode(React.refs.someref).value)
  }

  changeContent(e) {
    this.setState({inputContent: e.target.value})
  } 

  render() {
    return (
      <div>
        <h4>The input form is here:</h4>
        Title: 
        <input type="text" ref="someref" value={this.inputContent} 
          onChange={this.changeContent} /> 
        <button onClick={this.sendContent}>Submit</button>
      </div>
    )
  }
}

export default SomeClass

2.Bind when it is called

import React from 'react'

class SomeClass extends React.Component {
  constructor(props) {
    super(props)
    this.state = {inputContent: 'startValue'}
  }

  sendContent(e) {
    console.log('sending input content '+React.findDOMNode(React.refs.someref).value)
  }

  changeContent(e) {
    this.setState({inputContent: e.target.value})
  } 

  render() {
    return (
      <div>
        <h4>The input form is here:</h4>
        Title: 
        <input type="text" ref="someref" value={this.inputContent} 
          onChange={this.changeContent} /> 
        <button onClick={this.sendContent.bind(this)}>Submit</button>
      </div>
    )
  }
}

export default SomeClass

3.By using Arrow functions

import React from 'react'

class SomeClass extends React.Component {
  constructor(props) {
    super(props)
    this.state = {inputContent: 'startValue'}
  }

  sendContent(e) {
    console.log('sending input content '+React.findDOMNode(React.refs.someref).value)
  }

  changeContent(e) {
    this.setState({inputContent: e.target.value})
  } 

  render() {
    return (
      <div>
        <h4>The input form is here:</h4>
        Title: 
        <input type="text" ref="someref" value={this.inputContent} 
          onChange={this.changeContent} /> 
        <button onClick={()=>this.sendContent()}>Submit</button>
      </div>
    )
  }
}

export default SomeClass
1

We need to bind the event function with the component in constructor as follows,

import React from 'react'

class SomeClass extends React.Component {
  constructor(props) {
    super(props)
    this.state = {inputContent: 'startValue'}
    this.changeContent = this.changeContent.bind(this);
  }

  sendContent(e) {
    console.log('sending input content '+React.findDOMNode(React.refs.someref).value)
  }

  changeContent(e) {
    this.setState({inputContent: e.target.value})
  } 

  render() {
    return (
      <div>
        <h4>The input form is here:</h4>
        Title: 
        <input type="text" ref="someref" value={this.inputContent} 
          onChange={this.changeContent} /> 
        <button onClick={this.sendContent}>Submit</button>
      </div>
    )
  }
}

export default SomeClass

Thanks

1

My recommendation is use arrow functions as a properties

class SomeClass extends React.Component {
  handleClick = () => {
    console.log(this); // the React Component instance
  }
  render() {
    return (
      <button onClick={this.handleClick}></button>
    );
  }
}

and do not use arrow functions as

class SomeClass extends React.Component {
      handleClick(){
        console.log(this); // the React Component instance
      }
      render() {
        return (
          <button onClick={()=>{this.handleClick}}></button>
        );
      }
    }

because second approach will generate new function every render call in fact this means new pointer new version of props, than if you will later care about performance you are able use React.PureComponent or in React.Component you can override shouldComponentUpdate(nextProps, nextState) and shallow check when props arrived

1

You can solve this following these steps

Change sendContent function with

 sendContent(e) {
    console.log('sending input content '+this.refs.someref.value)
  }

Change render function with

<input type="text" ref="someref" value={this.state.inputContent} 
          onChange={(event)=>this.changeContent(event)} /> 
   <button onClick={(event)=>this.sendContent(event)}>Submit</button>
1

We have to bind our function with this to get instance of the function in class. Like so in example

<button onClick={this.sendContent.bind(this)}>Submit</button>

This way this.state will be valid object.

1

if anyone will ever reach this answer, here is a way to bind all of the functions without needing to bind them manually

in the constructor():

for (let member of Object.getOwnPropertyNames(Object.getPrototypeOf(this))) {
    this[member] = this[member].bind(this)
}

or create this function in a global.jsx file

export function bindAllFunctions({ bindTo: dis }) {
for (let member of Object.getOwnPropertyNames(Object.getPrototypeOf(dis))) {
    dis[member] = dis[member].bind(dis)
    }
}

and in your constructor() call it like:

bindAllFunctions({ bindTo: this })
0

This issue is happening because this.changeContent and onClick={this.sendContent} are not bound to this of the instance of the component .

There is another solution (In addition to use bind() in the constructor() ) to use the arrow functions of ES6 which share the same lexical scope of the surrounding code and maintain this , so you can change your code in render() to be :

render() {
    return (

        <input type="text"
          onChange={ () => this.changeContent() } /> 

        <button onClick={ () => this.sendContent() }>Submit</button>

    )
  }
1
  • 3
    This is also considered a bad practice, since you are creating a new function every time the component renders. You can define your functions on your ES6 classes by const changeContent = () => {...} to automatically bind it to the class itself .. Commented Oct 10, 2016 at 15:58
0

Hello if you want to dont care about binding yourself your function call. You can use 'class-autobind' and import it like that

import autobind from 'class-autobind';

class test extends Component {
  constructor(props){
  super(props);
  autobind(this);
}

Dont write autobind before the super call because it will not work

0

In case you want to keep the bind in constructor syntax, you can use the proposal-bind-operator and transform your code like follow :

constructor() {
  this.changeContent = ::this.changeContent;
}

Instead of :

constructor() {
  this.changeContent = this.changeContent.bind(this);
}

much simpler, no need of bind(this) or fatArrow.

0

this problem happen after react15.0 ,which event handler didn't auto bind to the component. so you must bind this to component manually whenever the event handler will be called.


there are several methods to solve the problem. but you need to know which method is best and why? In general, we recommend that binding your functions in the class constructor or use a arrow function.

// method 1: use a arrow function
    class ComponentA extends React.Component {
      eventHandler = () => {
        console.log(this)
      }
      render() {
        return ( 
        <ChildComponent onClick={this.eventHandler} /> 
        );
      }

// method 2: Bind your functions in the class constructor.
    class ComponentA extends React.Component {
      constructor(props) {
        super(props);
        this.eventHandler = this.eventHandler.bind(this);
      }
      render() {
        return ( 
        <ChildComponent onClick={this.eventHandler} /> 
        );
      }

these two methods will not creates a new function when the component render everytime. so our ChildComponent will not reRender becaue of the new function props change, or may produce the performance problem.

0

You are using ES6 so functions will not bind to "this" context automatically. You have to manually bind the function to the context.

constructor(props) {
  super(props);
  this.changeContent = this.changeContent.bind(this);
}
0

Your functions needs binding in order to play with state or props in event handlers

In ES5, bind your event handler functions only in constructor but don't bind directly in render. If you do binding directly in render then it creates a new function every time your component renders and re-renders. So you should always bind it in constructor

this.sendContent = this.sendContent.bind(this)

In ES6, use arrow functions

When you use arrow functions then you no need to do binding and you can also stay away from scope related issues

sendContent = (event) => {

}
0

Alexandre Kirszenberg is correct, But another important thing to pay attention to , is where you put your binding. I have been stuck with a situation for days(probably because I'm a beginner), but unlike others, I knew about bind(Which I had applied already) so I just couldn't get my head around why I was still having those errors. It turns out that I had the bind in wrong order.

Another is also perhaps the fact that I was calling the function within "this.state", which was not aware of the bind because it happened to be above the bind line,

Below is what I had(By the way this is my first ever posting, But I thought it was very important, as I couldn't find solution any where else):

constructor(props){
    super(props);

       productArray=//some array

    this.state={ 
        // Create an Array  which will hold components to be displayed
        proListing:productArray.map(product=>{return(<ProRow dele={this.this.popRow()} prodName={product.name} prodPrice={product.price}/>)})
    }

    this.popRow=this.popRow.bind(this);//This was the Issue, This line //should be kept above "this.state"
0

Solution:

  1. Without explicitly binding, bind with the method name you can use fat arrow functions syntax ()=>{} that maintains the context of this.
import React from 'react'

class SomeClass extends React.Component {
  constructor(props) {
    super(props)
    this.state = {
      inputContent: 'startValue'
    }
  }

  sendContent = (e) => {
    console.log('sending input content ',this.state.inputContent);
  }

  changeContent = (e) => {
    this.setState({inputContent: e.target.value},()=>{
      console.log('STATE:',this.state);
    })
  } 

  render() {
    return (
      <div>
        <h4>The input form is here:</h4>
        Title: 
        <input type="text" value={this.state.inputContent} 
          onChange={this.changeContent} /> 
        <button onClick={this.sendContent}>Submit</button>
      </div>
    )
  }
}

export default SomeClass

Other Solutions:

  1. Bind your functions in the class constructor.

  2. Bind your functions in the JSX Template escaping braces {} {this.methodName.bind(this)}

0

bind(this) can fix this issue, and nowadays we can use another 2 ways to achieve this if you don't like using bind .

1) As the traditional way, we can use bind(this) in the constructor, so that when we use the function as JSX callback, the context of this is the class itself.

class App1 extends React.Component {
  constructor(props) {
    super(props);
    // If we comment out the following line,
    // we will get run time error said `this` is undefined.
    this.changeColor = this.changeColor.bind(this);
  }

  changeColor(e) {
    e.currentTarget.style.backgroundColor = "#00FF00";
    console.log(this.props);
  }

  render() {
    return (
      <div>
        <button onClick={this.changeColor}> button</button>
      </div>
    );
  }
}

2) If we define the function as an attribute/field of the class with arrow function, we don't need to use bind(this) any more.

class App2 extends React.Component {
  changeColor = e => {
    e.currentTarget.style.backgroundColor = "#00FF00";
    console.log(this.props);
  };
  render() {
    return (
      <div>
        <button onClick={this.changeColor}> button 1</button>
      </div>
    );
  }
}

3) If we use arrow function as JSX callback, we don't need to use bind(this) either. And further more, we can pass in the parameters. Looks good, isn't it? but its drawback is the performance concern, for details please refer ReactJS doco.

class App3 extends React.Component {
  changeColor(e, colorHex) {
    e.currentTarget.style.backgroundColor = colorHex;
    console.log(this.props);
  }
  render() {
    return (
      <div>
        <button onClick={e => this.changeColor(e, "#ff0000")}> button 1</button>
      </div>
    );
  }
}

And I have created a Codepen to demo these code snippets, hope it helps.

Not the answer you're looking for? Browse other questions tagged or ask your own question.