JSFiddle - React, Tailwind, and code Playground

JavaScript

var htmlstring = "<div id='1'></div><input type='text' id='2'/>";

var $dom = $('<div>').html(htmlstring);

$('[id]', $dom).each(function() {
    $(this).attr('id', 'num_' + $(this).attr('id'));
});

htmlstring = $dom.html();

alert(htmlstring);