JSFiddle - React, Tailwind, and code Playground

JavaScript

var myArr = ['Foo', 'Bar'];
var contenthtml = '<p>Foo</p>\n'
    + '<p>Lorem ipsum dolor sit amet</p>\n'
    + '<p>Lorem <b>ipsum</b> dolor sit amet</p>\n'
    + '<p>Lorem ipsum dolor sit amet</p>\n'
    + '<p>Bar</p>\n'
    + '<p>Lorem ipsum dolor sit amet</p>';
var elements = $.parseHTML(contenthtml);
var tmp = '';
$.each(elements, function(index, element) {
    $.each(myArr, function(i, e) {
        if (element.innerHTML == e) {
            elements[index] = $('<h1>' + e + '</h1>').get(0);
            return;
        }
    });
    if (elements[index].outerHTML) {
        tmp += elements[index].outerHTML + '\n';
    }
});
contenthtml = '<div class="foo">' + tmp + '</div>';
console.log(contenthtml);