JSFiddle - React, Tailwind, and code Playground

HTML

<input type="date" id="birthday" />

JavaScript

function valueifyDate(date){
	if(typeof date == 'object'){
  	return date.getTime();
  }else{
  	return new Date(date).getTime();
  }	
}

var bday = document.getElementById('birthday');
bday.addEventListener("change", function(e){
  var today = new Date();
  if(valueifyDate(today) < valueifyDate(e.target.value)){
  	console.log("younger than today");
  }
})