These are some best practice suggestions for upstreams which can help in Debian packages.

Stick to common build tools

If you use common tools like babel, webpack, rollup, gulp etc with recent versions and avoid using exotic tools not widely used, that will be a big step. If you can reduce the number of tools you need to build, that would be awesome. If webpack alone can do something, please don't use gulp and webpack (or rollup and webpack).

Stick to widely implemented features

Just support the node versions currently supported by node upstream and avoid babel if possible, ie, stick to features provided by node proper as much as possible. If buble and babel can transpile your project and not tied to a specific babel plugin, that is awesome, basically stick to established standards as much as possible and avoid using features that are still proposals (just stick to @babel/env).

Use standard interfaces to build tools

Please avoid using custom build scripts and use standard configuration files like webpack.config.js or rollup.config.js. Avoid using gruntfile or gulpfile if you can run commands directly from package.json#scripts.

Support building from source

Be responsive to requests for updating your build toolchain. Don't insist on using only the files you generated. Don't stick to versions that are released many years ago since you are afraid of changing what worked once. Being able to build from source with recent versions of build tools is not a weird request.

Add enough tests

Add enough tests so you can confidently change things and be sure not to break things. Again stick to commonly used testing frameworks and please don't invent your own framework.