A HTML-only approach could work in your case, as well.
Assumptions:

1. the code showcased in the question is not inside a eventHandler
2. you want the HTML to handle video source at page load

The best reference is here: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/source#using_the_media_attribute_with_video

Note: Avoid parsing markup through JS as it is considered insecure.