JSFiddle - React, Tailwind, and code Playground

HTML

<div class="bob" data-xyz="fish"></div>
<div class="bob" data-xyz="dog"></div>
<div class="bob" data-xyz="fish"></div>
<div class="bob" data-xyz="cat"></div>
<div class="bob" data-xyz="fish"></div>

JavaScript

var items = {};
$('div.bob').each(function() {
    items[$(this).attr('data-xyz')] = true; 
});

var result = new Array();
for(var i in items)
{
    result.push(i);
}
alert(result);