JSFiddle - React, Tailwind, and code Playground

HTML

<span id="id1">1</span>
<span id="id2">2</span>
<span id="id3">3</span>
<span id="id5">5</span>
<span id="id4">4</span>

JavaScript

// create an array
    var ar = new Array();
    // for each element with id that starts with 'id'
    $('[id^="id"]').each(
         function(){
                    // add it to the array (only its numeric part)
                    ar.push(
                            // extract the numeric part to be added in the array
                            parseInt( $(this).attr('id').replace('id','') )
                          );
                   });
    // find the max value in the array 
    alert('id' + Math.max.apply( Math, ar ));