JSFiddle - React, Tailwind, and code Playground
HTML
<a href=" http://www.amazon.de/dp/B00VB2ISDM/ ">link1</a>
<a href="www.amzn.com">link2</a>
<a href="www.google.com">link3</a>JavaScript
$("a").each(function(){
var atag = 'amztag-21';
var ahref = $(this).attr("href");
if(ahref.indexOf('amazon') !== -1 || ahref.indexOf('amzn') !== -1){
$(this).attr("href",ahref+"?tag="+atag);
}
});