Draft.js Fiddle

A fiddle to repro issues in Draft.js

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.3.0/react.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.3.0/react-dom.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/immutable/3.8.1/immutable.js"></script>
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/draft-js/0.7.0/Draft.css">
<script src="https://cdnjs.cloudflare.com/ajax/libs/draft-js/0.10.0/Draft.js"></script>
<div id="react-root"></div>

CSS

body {
  font-family: Helvetica, sans-serif;
}

.container-root {
  border: 1px solid black;
  padding: 5px;
  margin: 5px;
}

Babel + JSX

const {Editor, EditorState} = Draft;

const MAX_LENGTH = 10;

class Container extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      editorState: EditorState.createEmpty()
    };
  }
  render() {
    return (
      <div className="container-root">
        <Editor 
          placeholder="Type away :)"
          editorState={this.state.editorState}
          handleBeforeInput={this._handleBeforeInput}
          handlePastedText={this._handlePastedText}
          onChange={this._handleChange}
        />
      </div>
    );
  }

  _handleBeforeInput = () => {
  	const currentContent = this.state.editorState.getCurrentContent();
    const currentContentLength = currentContent.getPlainText('').length

  	if (currentContentLength > MAX_LENGTH - 1) {
    	console.log('you can type max ten characters');

    	return 'handled';
    }
  }
  
  _handlePastedText = (pastedText) => {
  	const currentContent = this.state.editorState.getCurrentContent();
    const currentContentLength = currentContent.getPlainText('').length

  	if (currentContentLength + pastedText.length > MAX_LENGTH) {
    	console.log('you can type max ten characters');

    	return 'handled';
    }
  }
  
  _handleChange = (editorState) => {
    this.setState({ editorState });
  }
}

ReactDOM.render(<Container />, document.getElementById('react-root'))