JSFiddle - React, Tailwind, and code Playground

HTML

<a href="http://site.com/any/different/folders/picture_name.jpg">Go and win</a>

JavaScript

$('a').attr('href', function(i,attr) {
    var index = attr.lastIndexOf('/') + 1;
    return attr.substr(0,index) + 'user_' + attr.substr(index);
});