JSFiddle - React, Tailwind, and code Playground

HTML

<a href="http://google.com" target="_blank">Google</a>
<a href="/">Home</a>
<a href="http://www.gusdecool.com/">Home</a>
<a href="contactus.html">Contact Us</a>

JavaScript

var as = document.getElementsByTagName('a');
var re = /https?:\/\/([^\/]*)\//;
for (var i = 0, l = as.length; i < l; i++) {
    var href = as[i].href;
    var matches = href.match(re);
    if (matches[1] && matches[1] != "fiddle.jshell.net") {
        as[i].setAttribute("target","_blank");
    }
}
console.log(as);