JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
    <li id="pic_0">
        <img src="http://localhost/wpff/wp-content/themes/twentyeleven/images/family/small/012_family-portrait_people_sea.jpg" name="012_family-portrait_people_sea.jpg" data-horz="y">
    </li>
    <li id="pic_1">
        <img src="http://localhost/wpff/wp-content/themes/twentyeleven/images/family/small/011_family-portrait_people_sea.jpg" name="011_family-portrait_people_sea.jpg" data-horz="y">
    </li>
    <li id="pic_2">
        <img src="http://localhost/wpff/wp-content/themes/twentyeleven/images/family/small/010_family-portrait_mother-son_sea.jpg" name="010_family-portrait_mother-son_sea.jpg" data-horz="y">
    </li>
</ul>

JavaScript

var Bigpic = "012_family-portrait_people_sea.jpg";
var horz = $('[name="'+Bigpic + '"]').data('horz');
alert(horz);