JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" id="input-url" placeholder="Enter URL here">
<button id="check-url" >Check</button>

JavaScript

var $btnCheck = document.getElementById('check-url'),
   $URLregX = /^https?:\/\/www\.(?:[a-z0-9]-?)+[^-\.]\.[a-z]{2,15}(?:\.[a-z]{2})?$/i;

$btnCheck.addEventListener('click', function(){
	var $URLtext = document.getElementById('input-url').value;
	console.log($URLregX.test($URLtext));
	if( !$URLregX.test($URLtext) ){
  	alert('Please enter a valid URL');
  } else {
  	alert('Thank you');
  }
});