add id in jquery

JavaScript
$('element').attr('id', 'value');TO add dynamically:
let $id=0;
$('ul li').each(()=>{
///use this also $('ul').children("li").each(function()=>{/// same below code})
  ///this will select the element under current selection, 
  ///THis outside the function relates or selects body, inside the function 
  /// denotes the selector php and js in think all library may be syntax 
  ///get vary
  $(this).attr('id','id'+$id)
  $i=$i+1
})
using js
///place the script just above to </body>
const s=document.getElementsByTagName('li');
len=s.length;
console.log(len)
for(let i=0;i<len;i++){
  s[i].id="id"+i;
}

$( ".inner" ).append( "<p>Test</p>" );
$( "li" ).add( document.getElementsByTagName( "p" )[ 0 ] )
  .css( "background-color", "red" );
<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>add demo</title>
  <script src="https://code.jquery.com/jquery-3.5.0.js"></script>
</head>
<body>
 
<p>Hello</p>
<span id="a">Hello Again</span>
 
<script>
var collection = $( "p" );
// Capture the new collection
collection = collection.add( document.getElementById( "a" ) );
collection.css( "background", "yellow" );
</script>
 
</body>
</html>
<ul>
  <li>list item 1</li>
  <li>list item 2</li>
  <li>list item 3</li>
</ul>
<p>a paragraph</p>
Source