JSFiddle - React, Tailwind, and code Playground
JavaScript
var div = document.createElement('div');
div.innerHTML = '<a href="[nggallery id=xx]"><span class="shutterset"><img class="alignnone size-large wp-image-23067" title="Image Title" src="http://example.com/wp-content/uploads/2015/06/image-title.jpg" alt="" width="685" height="456" /></span></a>';
var a = div.querySelector('a');
document.body.innerHTML = a.attributes[0].nodeValue;