JSFiddle - React, Tailwind, and code Playground

HTML

<div id="2" class="maindiv">test</div>
<div id="5" class="maindiv">test</div>
<div id="3" class="maindiv">test</div>
<div id="1" class="maindiv">test</div> 
<div class="maindiv">test</div>     
<div id="4" class="maindiv">test</div>

JavaScript

function minMaxId(selector) {
    var min=null, max=null;
    $(selector).each(function() {
        var id = parseInt(this.id, 10);
        if (isNaN(id)) { return; }
        if ((min===null) || (id < min)) { min = id; }
        if ((max===null) || (id > max)) { max = id; }
    });
    return [min, max];
}

alert(minMaxId('div'));