First of all, note that this script is strongly inspired on @qerrant's BezierBlenderToUE script.
We adapted it to export json instead of csv.
This plug-in raises from the necessity of avoiding to handcraft bezier curves, mostly when they are related to some other geometry. Why can't we just export them as we do with our gltf models? Remember that gltf doesn't support bezier data like points + handles info.
There's where this plug-in comes very useful. Imagine you need a spline that travels through a castle model, to animate the camera position for example. Crafting that by hand might be a pain in the ass 😬. Now imagine that, for some reason, you update your castle model, remove some rooms here and there and scale some stuff, you have go back and update all the points by hand (again) to keep it consistent with the model. There's no reason to do that if you can just update it on Blender working on the same context 🙏🏼.
To use this plug-in just install it like any other custom Blender plug-in, it will add a new export type under File > Export > Bezier2JSON (.json).
If you don't know how to install a custom plug-in check this.
Once you have your bezier.json there's a piece of code that you'll need to parse into ThreeJS classes. You can get it in this example's code.
You can also see a demo of how it works in this lab's example.