Bazel integrates well with nixpkgs and npm with rules_nixpkgs [0] and rules_nodejs [1] respectively.

Tangentially related to package manager integration: Bazel can now build with CMake in-tree [2].

[0] https://github.com/bazelbuild/rules_nixpkgs/

[1] https://github.com/bazelbuild/rules_nodejs/

[2] https://github.com/bazelbuild/rules_foreign_cc/