JSFiddle - React, Tailwind, and code Playground

HTML

<div class="ref" id="14300"></div>
<div class="ref" id="14301"></div>
<div class="ref" id="14302"></div>

JavaScript

var biggestNum = 0;
	$('div[class^="ref"]').each(function(){
		var currentNum = (parseInt($(this).attr('id'), 10) +1);
		if(currentNum > biggestNum) {
			biggestNum = currentNum;
		}
	});
	
	alert(biggestNum);