JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" name="demo" />
<div id="punkt2">WEEE</div>

CSS

#punkt2{display:none;}

JavaScript

$("input[name=demo]").keypress(function(){
    var value = $(this).val();
  if(value.match(/^[a-z]{1}[0-9]{7}$/))
  {
    $("#punkt2").show();
  }else
  {
    $("#punkt2").hide();
  }
});