How do I set a ref when using react.createElement?

As of react v16.3, this.refs has been discouraged. One of the popular ways of doing it would be,

  const Comp = React.createElement(
                MyComp,
                {
                    props: myprops,
                    ref: ref => this.mycomp = ref
                }
            );

https://facebook.github.io/react/docs/top-level-api.html#react.createelement

ReactElement createElement(
  string/ReactClass type,
  [object props],
  [children ...]
)

The second parameter of the function is an optional props object for the component. Unless you want to refer to the props in the component as props.props you can splat the myProps object:

var comp = React.createElement(MyComp, { ...myprops, ref: "mycomp" });

class MyComp extends React.Component {
  constructor(props) {
    super(props);
    this.initialValue = props.initialValue;
    this.state = { value: this.initialValue };
    this.increment = this.increment.bind(this);
    this.reset = this.reset.bind(this);
  }
  
  increment() {
    this.setState({ value: this.state.value + 1 });
  }
  
  reset() {
    this.setState({ value: this.initialValue });
  }
  
  render() {
    return (
      <div className="child">
        <h1>Counter: {this.state.value}</h1>
        <button onClick={this.increment}>Increment</button>
      </div>
    );
  }
}

class App extends React.Component {
  constructor(props) {
    super(props);
    this.reset = this.reset.bind(this);
  }
  
  reset() {
    this.refs.mycomp.reset();
  }
  
  render() {
    const myProps = { initialValue: 1 };
    const Comp = React.createElement(MyComp, { ...myProps, ref: "mycomp" });
    return (
      <div className="parent">
        {Comp}
        <button onClick={this.reset}>Reset</button> Calls this.refs.mycomp.reset
      </div>
    );
  }
}

  
ReactDOM.render(<App />, document.getElementById('app'));
.parent {
  background-color: #555;
  color: #FFF;
  padding: 10px;
}

.child {
  background-color: #888;
  padding: 10px;
}

h1 {
  margin: 0;
}
<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="app"></div>