heic-to 1.6.6 (dist/csp/heic-to.js, unmodified)
License: GNU LGPL-3.0 (LICENSE.txt). It bundles libheif, also LGPL-3.0.
Source: https://github.com/hoppergee/heic-to
libheif source: https://github.com/strukturag/libheif
You may replace heic-to.js with your own build of the same interface.