How to apply method to AirDatepicker in my custom js file?

I have a AirDatepicker v3.3.5 defined in app.js file as :

window.dateRangePicker = new AirDatepicker('.date-range', {
    range: true,
    maxDate: new Date(),
    multipleDatesSeparator: ' - '
});

Looking at https://air-datepicker.com/examples docs
I need in my custom form.js to add to apply onSelect and update methods like

dpMin = new AirDatepicker('#el1', {
    onSelect({date}) {
        dpMax.update({
            minDate: date
        })
    }
})

But I failed it, as I tried :

window.dateRangePicker.onSelect({date}) {
    ...

};

But I got error :

Expecting new line or semicolon

Which syntax is valid ?

As mentioned in the comments, Document says we can pass the onSelect method inside the options at the time of initialisation but they don't have onSelect method on that created object itself.

When i checked and traced the assigned object i find that we can utilise the functions exposed as part of created object. We can assign the method after initialisation like below.

You can try something like this.

window.dateRangePicker.opts.onSelect = ({date}) => {
  console.log(date);
}