Cannot read property 'state' of null

Question

I have an input and a button

<input className="form-control" value={this.state.sentence} onChange={this.onChange}/>
<button type="button" onClick={this.handleSentence}></button>

I have binded both functions in constructor.

onChange(e) {this.setState({sentence: e.target.value});}

handleSentence(e) {console.log('string -->',this.state.sentence)}

on handleSentence function the log returns Cannot read property 'state' of null.

but in render(let{sentence}=this.state) returns the correct value and also I see what I type in input

here is the constructor:

class SentenceForm extends Component {
    constructor(props) {
        super(props)
        this.state = {
            sentence: '',
            splitedSentenceArray:[]
        }
        this.onChange = this.onChange.bind(this);
        this.onClick = this.handleSentence.bind(this);
    }

Answer 1

It should look like this:

<input className="form-control" value={this.state.sentence} onChange={this.onChange}/>
<button type="button" onClick={this.onClick}></button>

You bound handleSentence method to this.onClick. That was wrong.

Answer 2

The best practise is to keep the function name same when you are binding. It avoids unnecessary confusion as in your case. You had done binding of handleSentence function by a different name but were still calling it by the same name so in your case the function was being called but since it was bound by a different name it did not refer to the correct context, where state is present.

class SentenceForm extends Component {
    constructor(props) {
        super(props)
        this.state = {
            sentence: '',
            splitedSentenceArray:[]
        }
        this.onChange = this.onChange.bind(this);
        this.handleSentence = this.handleSentence.bind(this);
    }