JSFiddle - React, Tailwind, and code Playground

HTML

<textarea id="input" style="width:100%; height:200px; resize:none;" wrap="off">8000
8000
8000
8001
8001
8002
8003
8004
8004
8005</textarea>
<textarea id="output" style="width:100%; height:200px; resize:none;" wrap="off"></textarea>

<input type="button" value="generate" id="generatebutton" />

JavaScript

$('#generatebutton').on('click', function(){
		var arr = $('#input').val();
			arr = arr.replace(/\n/g, ', ');
			arr = arr.split(',');
	  var newarr = []; check = 0; count = 0;
	      for(i=0; i<arr.length; i++){
	      if(check != arr[i]){ count = 1; check = arr[i]; } else { count++; }
	      newarr.push(check + '.' + count);
	  }
     
	  newarr = newarr.join().replace(/, /g, '\n');
    
		$('#output').val(newarr);
});