ChangeStyleOfText.html

<!--Write a Javascript (JS) function changeAll() that restyles all numbers in a specified DIV 
element containing some text when a button is clicked by the user. The restyling should 
underline all numbers, for example, “There are 7 words in this sentence!” would be changed 
to “There are 7(underline) words in this sentence!”. Please provide the HTML code for the button that
is used to invoke changeAll(). -->

<!DOCTYPE html>
<html>
<head>
<style type="text/CSS">
body{
font-family:Times New Roman;
font-size:15px;

}
textarea {
  font-family:Times New Roman;
  font-size:15px;
  border:2px solid black;
  width: 300px;
  height: 217px;
  padding:10px;
 }


span{
  text-decoration: underline;
}

button{
  text-align: center;
  width: 100px; 
}
</style>
<script>

function underlineNumbers(){

  var szukane = document.getElementById("input").innerHTML;
  var look = "123456789";
  
  var wyswietl="";
  for(i=0; i<szukane.length; i++)
  {  
      if(szukane.charAt(i).match(/^\d+$/))
    { wyswietl= wyswietl+"<span>"+szukane.charAt(i)+"</span>";}
    else{wyswietl= wyswietl+szukane.charAt(i);}
  }
 

  document.getElementById("input").innerHTML = wyswietl;

}

</script>

</head>
<body>

<div id="input">
34222 is a truth 3 </div>

<button onClick="underlineNumbers()">underNum</button>

</body>
</html>