Why can't you use npm modules via a CDN like https://unpkg.com/? Add a JS file that downloads whatever package you need and then use them in that JS file? Have your HTML page load that file via a script tag (you can also have the HTML file load the packages in a script tag) and then you're off to the races.
That's what I did before npm came around, but proper package management, hot reload, test runners etc. are creature comforts I'd hate to do without these days. Keeping dependencies up to date when getting them from a CDN is pretty cumbersome.
