We developed JavaScript for Classic UI that executes a call out to Segment as a means of establishing and tracking presence for our Users. Since this does not attempt any DOM manipulation, it works fine in a Visualforce Area component on the left nav bar in Classic, and loads for most tabs and pages (not Reports or Dashboards or Setup, but that's OK). We are able to extract and send User ID, system time and even salesforce.com URL (for record IDs, etc.) for most every page load a user performs. And it can all be done with just one script in one location, the Left column of Home Page Layouts.
Is there an equivalent to the Left Nav bar in Lightning that would allow a Visualforce Area to exist on (most) any loaded page? Or another way to similarly execute JavaScript on every page load...without editing every layout to include it?