Systems

Node.js is structured as a set of subsystems that together produce the JavaScript runtime. This section covers the major ones. Each page focuses on a single subsystem: the C++ host code, the JS-side wrappers, the public API surface, and where to start when changing it.

Map

Subsystem	Where it lives
Bootstrap and startup	src/node.cc, src/node_main_instance.cc, lib/internal/bootstrap/, lib/internal/main/
Module loaders	lib/internal/modules/cjs/, lib/internal/modules/esm/, lib/internal/modules/typescript.js, src/module_wrap.cc
Streams	lib/internal/streams/, lib/stream/, src/stream_base.cc, src/stream_pipe.cc
Errors and validators	lib/internal/errors.js, lib/internal/validators.js, src/node_errors.{cc,h}
File system	lib/fs.js, lib/internal/fs/, src/node_file.cc, src/node_dir.cc
Net, TCP, TLS, DNS	lib/net.js, lib/tls.js, lib/dns.js, src/tcp_wrap.cc, src/udp_wrap.cc, src/cares_wrap.cc, src/crypto/crypto_tls.cc
HTTP / HTTP/2 / HTTP/3 / QUIC	lib/_http_*.js, lib/http2.js, lib/internal/http2/, lib/quic.js, src/node_http_parser.cc, src/node_http2.cc, src/quic/
Crypto and TLS	lib/crypto.js, lib/internal/crypto/, src/crypto/, deps/ncrypto/, deps/openssl/
Child processes and worker threads	lib/child_process.js, lib/worker_threads.js, lib/internal/child_process.js, lib/internal/worker/, src/spawn_sync.cc, src/process_wrap.cc, src/node_worker.cc
Diagnostics	lib/async_hooks.js, lib/diagnostics_channel.js, lib/perf_hooks.js, lib/trace_events.js, src/async_wrap.cc, src/inspector/, src/tracing/, src/node_perf.cc, src/node_report.cc
Permission Model	src/permission/, lib/internal/process/permission.js
Test runner	lib/test.js, lib/internal/test_runner/
SQLite	lib/sqlite.js, src/node_sqlite.cc, deps/sqlite/
Single Executable Applications (SEA)	lib/sea.js, src/node_sea.cc, src/node_sea_bin.cc, deps/postject/, deps/LIEF/
Node-API	src/js_native_api*, src/node_api*, doc/api/n-api.md
URL and URLPattern	lib/url.js, lib/internal/url.js, src/node_url.cc, src/node_url_pattern.cc, deps/ada/
Inspector	src/inspector/, src/inspector_*.{cc,h}, lib/inspector.js, lib/internal/inspector/
WASI	lib/wasi.js, src/node_wasi.cc, deps/uvwasi/
FFI	lib/ffi.js, lib/internal/ffi-shared-buffer.js, src/ffi/, src/node_ffi.cc, deps/libffi/

For lower-level building blocks (Environment, Realm, BaseObject, AsyncWrap, snapshots), see Primitives.