Read more option in php with collapse

gistfile1.txt

<p> 
<?php    

$string = strip_tags($property['description_en']);
$n=strlen($string);
if ($n > 500) {

    // truncate string
   
    $newstring = substr($string, 0, 500);
    
    $newstring .= '<span id="more">... <a href="" class="bold" id="viewmore"  data-toggle="collapse" data-target="#demo" >Read More</a></span>';
    
    $balance = substr($string,500, $n);

    echo $newstring;
}
else
{
  echo $string;
}

?><span id="demo" class="collapse"><?php echo $balance; ?></span>

</p>

<!--   JQuery -->
<script>

  $("#viewmore").click(function(){
  $("#more").hide();
   });
   
</script>