title: Why do I need 'bind(this)' in the example above
body: <p>I begin read the Reactjs and faced with a question in example. In constructor will add</p>
  
  <pre><code>this.handleChange = this.handleChange.bind(this);
  this.handleSubmit = this.handleSubmit.bind(this);
  </code></pre>
  
  <p>But I can't understand, what role do they play out and why are they needed? Code will work, if a method is change to the arrow func. Thanks. </p>
  
  <p>Full example:</p>
  
  <pre><code>class NameForm extends React.Component {
     constructor(props) {
        super(props);
        this.state = {value: ''};
  
        this.handleChange = this.handleChange.bind(this);
        this.handleSubmit = this.handleSubmit.bind(this);
      }
  
      handleChange(event) {
          this.setState({value: event.target.value});
      }
  
      handleSubmit(event) {
          alert('A name was submitted: ' + this.state.value);
          event.preventDefault();
      }
  
      render() {
          return (
             &lt;form onSubmit={this.handleSubmit}&gt;
                &lt;label&gt;
                  Name:
                     &lt;input type="text" value={this.state.value} onChange={this.handleChange} /&gt;
                 &lt;/label&gt;
                 &lt;input type="submit" value="Submit" /&gt;
             &lt;/form&gt;
          );
      }
     }
  </code></pre>