JSFiddle - React, Tailwind, and code Playground

HTML

<input type="button" class="extension" value=".com" />
<input type="button" class="extension" value=".net" />
<input type="button" class="extension" value=".info" />
<input type="button" class="extension" value=".org" />
<br><br>
<a href="www.example.com" id="myLink" >www.example.com</a>

JavaScript

var extensions = document.getElementsByClassName("extension");

for (var i = 0; i < extensions.length; i++) {
    extensions[i].onclick = function() {
        var defaultAddress = "www.example";
        var myLink = document.getElementById("myLink");
        myLink.href = defaultAddress + this.value;
        myLink.innerText = defaultAddress + this.value;
    }
}