There are several dependencies that Node.js relies on to work the way it does.
Another important dependency is libuv, a C library that is used to abstract non-blocking I/O operations to a consistent interface across all supported platforms. It provides mechanisms to handle file system, DNS, network, child processes, pipes, signal handling, polling and streaming. It also includes a thread pool for offloading work for some things that can't be done asynchronously at the operating system level.
HTTP parsing is handled by a lightweight TypeScript and C library called llhttp. It is designed to not make any syscalls or allocations, so it has a very small per-request memory footprint.
resolve() family of functions. The
lookup() function, which is what the rest of core uses, makes use of threaded
getaddrinfo(3) calls in libuv. The reason for this is that c-ares supports /etc/hosts, /etc/resolv.conf and /etc/svc.conf, but not things like mDNS.
OpenSSL is used extensively in both the
crypto modules. It provides battle-tested implementations of many cryptographic functions that the modern web relies on for security.
For fast compression and decompression, Node.js relies on the industry-standard zlib library, also known for its use in gzip and libpng. Node.js uses zlib to create sync, async and streaming compression and decompression interfaces.
Node.js is all about modularity, and with that comes the need for a quality package manager; for this purpose, npm was made. With npm comes the largest selection of community-created packages of any programming ecosystem, which makes building Node.js apps quick and easy.
The build system is handled by gyp, a python-based project generator copied from V8. It can generate project files for use with build systems across many platforms. Node.js requires a build system because large parts of it — and its dependencies — are written in languages that require compilation.
Native code can be tested using gtest, which is taken from Chromium. It allows testing C/C++ without needing an existing node executable to bootstrap from.