JSFiddle - React, Tailwind, and code Playground

by salt

HTML

<div data-customized="2" class="maindiv">test</div>
<div data-customized="5" class="maindiv">test</div>
<div data-customized="3" class="maindiv">test</div>
<div data-customized="1" class="maindiv">test</div> 
<div class="maindiv">test</div>     
<div data-customized="4" class="maindiv">test</div>

JavaScript

function minMaxDataValue(selector) {
	    var min=null, max=null;
	    $(selector).each(function() {
	        var id = parseInt(this.dataset.customized, 10);
	        if (isNaN(id)) { return; }
	        if ((min===null) || (id < min)) { min = id; }
	        if ((max===null) || (id > max)) { max = id; }
	    });
	    return {min:min, max:max};
	}

alert(minMaxDataValue('div[data-customizedw]').min);