JSFiddle - React, Tailwind, and code Playground

JavaScript

var data = "<div id='1'></div><div id='asdf'><input type='text' id='2'/></div>",
    numCompare = 23,
    div = document.createElement("div"),
    i, cur;

div.innerHTML = data;

function updateId(parent) {
    var children = parent.children;
    for (i = 0; i < children.length; i++) {
        cur = children[i];
        if (cur.nodeType === 1 && cur.id) {
            cur.id = cur.id + "_" + numCompare;
        }
        updateId(cur);
    }
}

updateId(div);

console.log(div);