JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://code.jquery.com/jquery-3.1.1.min.js"></script>
<div id="content" style="width: 100px">hello how are you? hello how are you? hello how are you?</div>

JavaScript

$(document).ready(function(){

  calculate = function(obj){
  	other = obj.clone();
    other.html('a<br>b').hide().appendTo('body');
    size = other.height() / 2;
    other.remove();
    return obj.height() /  size;
  }
  
  n = calculate($('#content'));
	alert(n + ' lines');
});