Where and how should I use Composer and the drupal-composer/drupal-project scaffold to install the required libraries? I installed Drupal 8 using the drupal-composer/drupal-project scaffold. I also installed the Devel module, and enabled its Webprofiler submodule.

Drupal status reports that Webprofiler needs:


D3.js library
highlight.js library


There's no libraries path in my Drupal installation.

As I'm using composer, both D3 and highlight have packages.


https://packagist.org/packages/mbostock/d3
https://packagist.org/packages/components/highlightjs


That's a preferred option.

Where do the libraries need to actually go when using this scaffold?  What path?

How do I correctly use Composer on this install to put them there?

Although Where should I download libraries for modules through composer? talks about it, it's only for the case of Composer Manager, which I am NOT using.
I use https://github.com/oomphinc/composer-installers-extender in my projects. It provides an composer installer for any package type.