Date picker Select Value

This is my test code:

$w.onReady(function () {
	//TODO: write your page related code here...
});

export function button1_click(event, $w) {
	//Add your code for this event here: 
	let date1 = $w("#datePicker1").value;
	let date2 = $w("#datePicker2").value;
	console.log(date_diff_indays(date1, date2));
}

export function date_diff_indays(date1, date2) {
    let dt1 = new Date(date1);
    let dt2 = new Date(date2);
    return Math.floor((Date.UTC(dt2.getFullYear(), dt2.getMonth(), dt2.getDate()) - Date.UTC(dt1.getFullYear(), dt1.getMonth(), dt1.getDate()) ) /(1000 * 60 * 60 * 24));
}

My page has two DatePickers (#datePicker1, #datePicker2).