> For the complete documentation index, see [llms.txt](https://docs.bashschool.in/v1/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.bashschool.in/v1/javascript/nodejs/packages.md). # Packages It is not productive to create everything from scratch. To increase productivity, **NodeJS** provides a mechanism to re-use previously written code. Such code is called a **package**. **Packages** can be installed via a commandline utility called **NPM**. **Packages** can be installed either *Global* or *local*. *Global* **packages** are installed on the machine and can be used from the command line or by all *Node apps* from that single installation. *Local* **packages** are installed with each *Node app* and cannot be used by other *Node apps*. When a *Node app* uses a **package**, it is called a *dependency*. This means that the *Node app* *depends* on the **package** in order to function properly. **Packages** can also use other **packages** as *dependencies*. **Packages** have *version numbers*. A *version number* indicates a specific iteration of code or features that the **package** supports. When a *Node app* *depends* on a specific *version* of a **package**, it avoids protentional problems and *conflicts* that might arise if there was no *versioning* in place. A *conflict* is when the *Node app* expects a certain feature or behavior that does not exist, or behaves differently than expected. #### To install a package: **NodeJS** provides a utility called `npm` that manages **packages**. With it you can install and remove **packages** easily. Each application should have a `package.json` file in its root directory. This file does not exist by default and must be created. To create it, simply type: `npm init` at the application root directory and follow the prompts. To add a **NodeJS** package, simply type: `npm install --save` at the application root directory. You can also remove a package via: `npm remove ` at the application root directory. When you get a *project* from GitHub the first time, it will usually contain the `package.json` file already. But the **packages** will usually not be included with the git repository. The **packages** will be listed in the `package.json` file. To install all the **package** dependencies, simply type: `npm intall` at the application root directory. Some **packages** will behave more like applications and others more like functionality for YOUR *Node app*. Those that behave more like applications (or utilities) must be installed *globally* and those that provide functionality as a part of YOUR *Node app* must be installed *locally*. To install a *global* **package**, simply type: `npm install -g ` anywhere. #### Exercises: * Create a new *Node app*. Add a `package.json` file * What is the purpose of the `main` key/value in the `package.json` file? * Install at least one **package** to the *project* * What happens if you omit `--save` when installing a **package**? * Install at least one **package** that is specific to the dev dependencies (HINT: testing usually will be dev specific (as in development, vs deployed to the end users and ready to use)) * Remove at least one **package** from the *project* * Validate that `package.json` reflects the change. If not, figure out why and try again * Install a specific *version* of a package to the *project* * What directory does NPM install *local* **packages** to? * What happens if you install a **package** at a different directory level than the application root directory? * How can you avoid uploading **package** files to github? (HINT: git.ignore... but how, specifically?) * Install a *global* package (`Nodemon`??) * Can a *global* **package** be a *dependency* to your *Node app*? Explain why or why not? * Launch your **NodeJS** app using the dev configuration. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.bashschool.in/v1/javascript/nodejs/packages.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.