java script call back function

If you want to access the actual DOM node, then ref is the only option. Generally refs are used to create uncontrolled components, where we let the DOM keep charge of the input's value, and get the value from our reference to the DOM node when we need it. You can't use value as a prop on these components, but you can use defaultValue to set their initial value:

class WithUncontrolledTextInput extends React.Component {
  constructor() {
    super();
    this.handleSubmit = this.handleSubmit.bind(this);
  }

  handleSubmit(e) {
    e.preventDefault();
    console.log(`The input value is ${this.textField.value}`);
  }

  render() {
    return (
      <form onSubmit={this.handleSubmit}>
        <input ref={input => this.textField = input} defaultValue='hello' />
        <input type='submit' value='Submit' />
      </form>
    );
  }
}

The alternative approach is to use a controlled component, where the current value of the input is stored within the component's state, and updated whenever the input value is updated.

class WithControlledTextInput extends React.Component {
  constructor() {
    super();
    this.state = {
      textField: 'hello'
    };
    this.handleSubmit = this.handleSubmit.bind(this);
    this.handleInput = this.handleInput.bind(this);
  }

  handleSubmit(e) {
    e.preventDefault();
    console.log(`The input value is ${this.state.textField}`);
  }

  handleInput(e) {
    this.setState({
      textField: e.target.value
    });
  }

  render() {
    return (
      <form onSubmit={this.handleSubmit}>
        <input value={this.state.textField} onChange={this.handleInput} />
        <input type='submit' value='Submit' />
      </form>
    );
  }
}