Introduce the npm package management tool, in which directory does it install the package under windows, what are the ways to use it to install the package, what are the functions of each, give examples

Introduction to npm package management tool

npm is a package management tool for Node.js, which is used to manage Node.js software packages (including installation, uninstallation, update, etc.). The full name of npm is Node Package Manager.

npm package installation directory under Windows

In the Windows system, the default directory for npm package installation is in the user's AppData directory, such as C:\Users\username\AppData\Roaming\npm.

How to install npm package

npm packages can be installed in the following ways:

1. Local installation

Run the following command in the project root directory:

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npm install <package_name>

This will install the specified package in the project's node_modules directory.

2. Global installation

Run the following command in any directory:

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npm install -g <package_name>

This will install the specified package in the global npm directory, which can be used anywhere.

3. Install locally and add it to package.json

Run the following command in the project root directory:

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npm install <package_name> --save

This will not only install the specified package in the node_modules directory of the project, but also add the information of the package to the dependencies field in the package.json file of the project.

4. Install locally and add it to the devDependencies of package.json

Run the following command in the project root directory:

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npm install <package_name> --save-dev

This will not only install the specified package in the node_modules directory of the project, but also add the package information to the devDependencies field in the project's package.json file.

Examples of npm packages

Take the local installation of the express package as an example, you can install it with the following command:

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npm install express

You can also add the package to your project's package.json file with the following command:

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npm install express --save

After the installation is complete, the express package will appear in the project's node_modules directory. The following code can be used to test whether the installation is successful:

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const express = require('express'); const app = express(); app.get('/', (req, res) => { res.send('Hello World!'); }); app.listen(3000, () => { console.log('Example app listening on port 3000!'); });

This code creates an Express application and starts it locally on port 3000. You can check that the application is working by visiting http://localhost:3000.