Indeterminate checkbox in React JSX

Question

How do I render an indeterminate checkbox via JSX?

Here's what I've tried:

function ICB({what}) {
  return <input type="checkbox"
                checked={what === "checked"} 
                indeterminate={what === "indeterminate"} />;
}

However, indeterminate is not an attribute on the HTMLElement, but a property. How do I set properties from React / JSX?

---

Solution:

As most of the answers below use findDOMNode or string refs, both of which are no longer considered good practice in React, I've written a more modern implementation:

function ICB() {
  const [state, setState] = React.useState(0);
  const indetSetter = React.useCallback(el => {
    if (el && state === 2) {
      el.indeterminate = true;
    }
  }, [state]);
  const advance = () => setState(prev => (prev + 1) % 3);
  
  return <input type="checkbox"
                checked={state === 1}
                ref={indetSetter}
                onClick={advance} />;
}
                
ReactDOM.render(<ICB />, document.getElementById("out"));

<div id="out"></div>

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.13.1/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.13.1/umd/react-dom.production.min.js"></script>

Answer 1

You can also use the ref function directly:

ReactDOM.render(
  <label>
    <input
      type="checkbox"
      ref={input => {
        if (input) {
          input.indeterminate = true;
        }
      }}
    />
    {' '}
    Un test
  </label>,
  document.getElementById('root')
);

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>
<div id="root"></div>

Answer 2

I would probably create a composite component that encapsulates the necessary hooks to set or unset the checkbox's indeterminate property. It looks like you're using ES2015 syntax, so I'll use some of those features here.

class IndeterminateCheckbox extends React.Component {
  componentDidMount() {
    if (this.props.indeterminate === true) {
      this._setIndeterminate(true);
    }
  }

  componentDidUpdate(previousProps) {
    if (previousProps.indeterminate !== this.props.indeterminate) {
      this._setIndeterminate(this.props.indeterminate);
    }
  }

  _setIndeterminate(indeterminate) {
    const node = React.findDOMNode(this);
    node.indeterminate = indeterminate;
  }

  render() {
    const { indeterminate, type, ...props } = this.props;
    return <input type="checkbox" {...props} />;
  }
}

// elsewhere

render() {
  return <IndeterminateCheckbox
           checked={this.props.state === "checked"} 
           indeterminate={this.props.state === "indeterminate"} />
}

Working example: https://jsbin.com/hudemu/edit?js,output