JSFiddle - React, Tailwind, and code Playground

by dandrade78

HTML

<textarea name="ta" id="ta" rows="4" cols="50">
 ABC
 DEF
 GHI
 </textarea>
 <input type="text" id="rt" name="textnumber" value="">

JavaScript

var tarea = document.querySelector('#ta')
    var input = document.querySelector('#rt')

    function update() {
      var res = (tarea.value.match(/\n/g)) ? tarea.value.match(/\n/g).length : 0;

      input.value = res;
    }

    tarea.addEventListener('input', update)