JSFiddle - React, Tailwind, and code Playground

HTML

<div>
    foo foo foo
</div>
<div>
    bar bar bar
</div>
<div>
    foo foo foo
</div>

CSS

#foo1{color:blue}
#foo2{color:red}
#foo3{color:blue}

JavaScript

var fooId = "foo";
for (var i = 0; i <= 2; i++) {
    document.getElementsByTagName('div')[i].setAttribute('id', fooId + (i + 1));
}