JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://code.jquery.com/jquery-3.2.1.min.js"></script>

JavaScript

var myCat = 'Cat1';
myXml = `<?xml version='1.0'?>
    <rss version="2.0">
        <channel>
            <title>Some Title</title>
            <pubDate>1/1/17 00:00:00</pubDate>
            <generator>SomeOne</generator>
            <item>
                <title>
                    Some Item Title 1
                </title>
                <link>http://example.org</link>
                <description>
                    Lorem ipsum ...
                </description>
                <pubDate>1/1/17 00:00:00</pubDate>
                <category>Cat1</category>
                <category>Cat2</category>
            </item>
            <item>
                <title>
                    Some Item Title 2
                </title>
                <link>http://example.org</link>
                <description>
                    Lorem ipsum ...
                </description>
                <pubDate>1/1/17 00:00:00</pubDate>
                <category>Cat2</category>
            </item>
            <item>
                <title>
                    Some Item Title 3
                </title>
                <link>http://example.org</link>
                <description>
                    Lorem ipsum ...
                </description>
                <pubDate>1/1/17 00:00:00</pubDate>
                <category>Cat1</category>
            </item>
        </channel>`;
        
 
rss = $(myXml);
rss.find('item').find('category').filter(':not(:contains('+ myCat +'))').parent().remove();

$(document.body).append('<pre>');
$(document.body).append($('<div/>').text(rss.find('item').html()).html());
$(document.body).append('</pre>');