JSFiddle - React, Tailwind, and code Playground

CSS

.c2 {
    color: red;
}

JavaScript

var linha = '<li id= "id1" class="c1"> ' +
    '<div id="id2">1</div>' +
    '<div id="id3">2</div></li>'
var temp = document.createElement('div');
temp.innerHTML = linha;
temp.querySelector('#id1').classList.add('c2');
document.body.innerHTML = temp.innerHTML;