How to display a variable in a variable?

Question

JavaScript

There is a code

var txt = содержит название ссылки
 var video =
        '        <div class="snippet">\n' +
        '          <div class="stage">\n' +
        '            <div class="dot-flashing"></div>\n' +
        '          </div>\n' +
        '        </div>\n' +
        '<video id=video5 width=600 height=300 class="video-js vjs-default-skin" placeinline>\n' +
        '    <source src='"https://youtube.com/..." type="application/x-mpegURL">\n' +
        '</video>';

how to display a txt variable instead of a link?
example to be

'    <source src='"txt." type="application/x-mpegURL">\n' +

Answer 1

Example https://codepen.io/wapster92/pen/qBrzqjq

Answer 2

'    <source src='"${txt}." type="application/x-mpegURL">\n' +