JSFiddle - React, Tailwind, and code Playground

HTML

<a data-agencyname="1"></a>
<a data-agencyname="2"></a>
<a data-agencyname="3"></a>
<a data-agencyname="4"></a>

JavaScript

var myVals = $('a[data-agencyname]').map(function(){
 return $(this).data('agencyname');
}).get();
console.log(myVals);