JSFiddle - React, Tailwind, and code Playground

HTML

<span id="s1">Lorem Ipsum</span>
<span id="s23">Lorem Ipsum</span>
<span id="s6">Lorem Ipsum</span>

JavaScript

var highest = 0;
$("span").each(function() {
    var id = parseInt(this.id.substring(1, this.id.length), 10);
    if(id > highest) {
        highest = id;
    }
});
alert(highest);