npm install installs dependencies into the node_modules/ directory, for the node project you're working on. You can call install on another node.js project (module), to install it as a dependency for your project.

npm run build does nothing unless you specify what "build" does in your package.json file. It lets you perform any necessary building/prep tasks for your project, prior to it being used in another project.

npm build is an internal command and is called by link and install commands, according to the documentation for build:

This is the plumbing command called by npm link and npm install.

You will not be calling npm build normally as it is used internally to build native C/C++ Node addons using node-gyp.

NPM in 2019

npm build no longer exists. You must call npm run build now. More info below.

TLDR;

npm install: installs dependencies, then calls the install from the package.json scripts field.

npm run build: runs the build field from the package.json scripts field.

NPM Scripts Field

https://docs.npmjs.com/misc/scripts

There are many things you can put into the npm package.json scripts field. Check out the documentation link above more above the lifecycle of the scripts - most have pre and post hooks that you can run scripts before/after install, publish, uninstall, test, start, stop, shrinkwrap, version.

To Complicate Things

• npm install is not the same as npm run install
• npm install installs package.json dependencies, then runs the package.json scripts.install
  • (Essentially calls npm run install after dependencies are installed.
• npm run install only runs the package.json scripts.install, it will not install dependencies.
• npm build used to be a valid command (used to be the same as npm run build) but it no longer is; it is now an internal command. If you run it you'll get: npm WARN build npm build called with no arguments. Did you mean to npm run-script build? You can read more on the documentation: https://docs.npmjs.com/cli/build or https://docs.npmjs.com/cli/v6/commands/npm-build

Extra Notes

There are still two top level commands that will run scripts, they are:

• npm start which is the same as npm run start
• npm test ==> npm run test

The main difference is:

npm install is a npm CLI-command which does the predefined thing i.e., as written by Churro, to install dependencies specified inside package.json.

npm run %command-name% or npm run-script %command-name% is also a CLI-command predefined to run your custom scripts with the name specified in place of "command-name". So, in this case npm run build is a custom script command with the name "build" and will do anything specified inside it (for instance echo 'hello world' given in below example package.json).

Points to note::

1. One more thing, npm build and npm run build are two different things, npm run build will do custom work written inside package.json and npm build is a pre-defined script (not available to use directly).

2. You cannot specify some thing inside custom build script (npm run build) script and expect npm build to do the same. Try following thing to verify in your package.json:

{
    "name": "demo",
    "version": "1.0.0",
    "description": "",
    "main": "index.js",
    "scripts": {
        "build": "echo 'hello build'"
    },
    "keywords": [],
    "author": "",
    "license": "ISC",
    "devDependencies": {},
    "dependencies": {}
}

and run npm run build and npm build one by one and you will see the difference. For more about commands kindly follow npm documentation.