Uncaught TypeError: Cannot read property 'toUpperCase' of undefined react state item

Question

I'm new to React and Javascript and I'm trying to render the following React component:

'use strict';
var React = require('react');
import ToReadList from './toreadlist.js';

var ToRead = React.createClass({
getInitialState: function() {
    return { bookTitles: [] };
},
handleSubmit: function(e) {
    e.preventDefault();
    this.state.bookTitles.push(React.findDOMNode(this.refs.bookTitleInput).value.trim());
    this.setState({items: this.state.bookTitles});
},
render: function() {
    return (<div>
        <form onSubmit={this.handleSubmit}><input type="text" ref="bookTitleInput"></input>
            <input type="submit"></input></form>
            <ToReadList bookTitles={this.state.bookTitles} />
    </div>
           );
}
});

module.exports = ToRead;

But I am having the following error on my console: "Uncaught TypeError: Cannot read property 'toUpperCase' of undefined"

I tried to debug (because the error is obscure to me and no line in my code is indicated) and noticed that this particular line:

this.state.bookTitles.push()

causes the error.

Please help!

Edit The error is caused by a webpack var injection function:

function autoGenerateWrapperClass(type) {
      return ReactClass.createClass({
        tagName: type.toUpperCase(),
        render: function() {
          return new ReactElement(
            type,
            null,
            null,
            null,
            null,
            this.props
          );
        }
      });
    }

Answer 1

findDOMNode() uses the toUpperCase() function which actually is called on a null.

Example

var x = null
x.toUpperCase()// results in this error.

If you could post the findDOMNode() code, we could trace out the error.

OR

Make sure that the toUpperCase() is called on a non-null object.