I looked at harfbuzzjs at one point when the work was making me cry. It looks very useful, but in the end I decided against using it. Partly because I'm keen to keep my library free of direct dependencies. But also because I know both Chromium and Firefox use Harfbuzz internally (I wonder what Safari uses instead?) and it annoys me that even with access to that tool, browsers still manage to make a mess of the Canvas Text Metrics interface[1].

People who develop canvas libraries soon learn that they don't get to play with Nice Things like consistency across browser implementations for the standards they've (allegedly) agreed to respect.

[1] - https://developer.mozilla.org/en-US/docs/Web/API/TextMetrics