npm install vs. update - what's the difference?

The difference between npm install and npm update:

package.json

{
  "name":          "my-project",
  "version":       "1.0",                             // install   update
  "dependencies":  {                                  // ------------------
    "already-installed-versionless-module":  "*",     // ignores   "1.0" -> "1.1"
    "already-installed-versioned-module":    "3.4.1"  // ignores   ignores
    "not-yet-installed-versionless-module":  "*",     // installs  installs
    "not-yet-installed-versioned-module":    "2.7.8"  // installs  installs
  }
}

Conclusion: The only big difference is that an already installed versionless module ...

• gets ignored by npm install
• gets updated by npm update

Why use npm install at all?

Because npm install does more when you look besides handling your dependencies in package.json. As you can see in npm install you can ...

• manually install node-modules
• set them as global (which puts them in the shell's PATH) using npm install -g <name>
• install certain versions described by git tags
• install from a git url
• force a reinstall with --force

npm install installs all modules that are listed on package.json file and their dependencies.

npm update updates all packages in the node_modules directory and their dependencies.

npm install express installs only the express module and its dependencies.

npm update express updates the express module and its dependencies.

So updates are for when you already have the module and wish to get the new version.

In most cases, this will install the latest version of the module published on npm.

npm install express --save

or better to upgrade module to latest version use:

npm install express@latest --save --force

--save: Package will appear in your dependencies.

More info: npm-install