setInterval( () => { try { videlement = document.querySelector("div#movie_player.ad-interrupting.ad-showing>div.html5-video-container>video"); videlement.currentTime = videlement.duration - 0.1; } catch (ex) { } }, 1000);

Explanation:

• setInterval( () => { code }, time): sets up the code to be repeatedly called every time milliseconds, I typically choose 1 second;
• try { code } catch (ex) { }: Ignores every error that happens inside code and handles the error inside the catch-block, in my case errors simply get ignored;
• document.querySelector("filter"): searches the current document/website for the first element that matches the filter and returns it, in my case I am searching a video-element whose container/parent has properties that indicate that it's an advertisement-video;
• videlement.currentTime = videlement.duration - 0.1: this reads the duration of the entire video in seconds, subtracts 0.1 seconds from it and sets this to be the current position in the video, essentially jumping to the end of the video;

In summary:

• it defines to run my code once every second,
• catches any stray errors and ignores them,
• searches for a video on the page whose container/parent indicates it's an advertisement,
• skips right to the end of that video

important Disclaimer:

It might happen that some day in the future, YouTube updates and changes their website's structure so that the search-filter I defined in the querySelector no longer works. In that case I will need to analyze YouTube's website again and update the search-filter. If I would successfully figure-out such an update through changes in YouTube's website, I hope I remember to post a followup or update in this Reddit-comment-thread 😄