The use of mongod and npm install in Node.js projects is as follows:
Use mongod when you want to start the MongoDB daemon process to run and manage the MongoDB database.
You need to run mongod whenever you want to interact with MongoDB, whether it's for development, testing, or production purposes.
Example: Suppose you are building a web application that requires a database to store user information. In this case, you would install and run MongoDB using mongod to provide the database functionality.
Use npm install when you want to install packages and dependencies for your Node.js project.
You run npm install after initializing a Node.js project with npm init or when you update your project's dependencies.
It reads the package.json file in your project directory to determine the required packages and their versions and installs them.
Example: Suppose you are building a web application using Express.js. You would use npm install to install the Express package and any other necessary packages your project depends on. For instance: