Dependencies
Dependencies are external packages of code your project uses to function.
In the Node.js ecosystem, developers use package.json at the root of
the project to declare a list of direct dependencies in the
dependencies (e.g., "express": "^4.18.0"). Each of those most
likely have transitive dependencies (i.e., express pulls in
body-parser, accepts, cookie respectively.). This list of packages,
and their dependencies are what constitutes a dependency tree for a
project.
Direct vs. transitive
| Type | What it is | Example |
|---|---|---|
| Direct | Listed in your package.json | express@^4.18.0 |
| Transitive | A dependency of one of your dependencies | body-parser (express needs it) |
For example, after running vlt install express typescript, this is
what your filesystem might look like:
- package.json list
express@^4.18.0directly - node_modules
- express ← direct dependency (you installed it)
- index.js
- node_modules
- body-parser ← transitive (express needs it)
- accepts ← transitive
- cookie ← transitive
- …
- typescript ← direct dependency (dev)
- express ← direct dependency (you installed it)
Dependency types
Packages in package.json can be declared under several categories:
Field in package.json | Purpose |
|---|---|
dependencies | Production dependencies needed at runtime |
devDependencies | Development-only tools (testing, building) |
peerDependencies | Expected host dependency (e.g., a component library that is built off react) |
optionalDependencies | Non-failing — install skipped if resolution fails |
Familiar with CSS selectors? Then you'll like DSS.
The vlt CLI provides handy colon-prefixed commands to query and filter
by dependency types
pseudo-state selectors like
:prod, :dev, :peer, and :optional.