Retrieving value from <select> with multiple option in React

The same way you do anywhere else, since you're working with the real DOM node as the target of the change event:

handleChange: function(e) {
  var options = e.target.options;
  var value = [];
  for (var i = 0, l = options.length; i < l; i++) {
    if (options[i].selected) {
      value.push(options[i].value);
    }
  }
  this.props.someCallback(value);
}

With Array.from() and e.target.selectedOptions you can perform a controlled select-multiple:

handleChange = (e) => {
  let value = Array.from(e.target.selectedOptions, option => option.value);
  this.setState({values: value});
}

target.selectedOptions return a HTMLCollection

https://codepen.io/papawa/pen/XExeZY

Easiest way...

handleChange(evt) {
  this.setState({multiValue: [...evt.target.selectedOptions].map(o => o.value)}); 
}