A package.json is a file that exists in the root directory of any Node.js project or module. It holds various metadata and configuration information about the project including:
1. Name of the project
2. Project version
3. Project description
4. List of dependencies and their versions
5. Scripts that are necessary for executing the program
6. Repository information
7. License information
8. And much more.
It is required for applications that need to be published on npm (Node Package Manager) registry.
To create a package.json, navigate to your project directory in command line or terminal and then type `npm init`. This command will ask you a bunch of questions like name, version, description, etc. and create a package.json file based on your answers.
To use it, you list your application’s dependencies in the package.json file in the dependencies section. Every time you run `npm install` in your project, Node.js looks in the package.json file and installs all the dependencies listed in it.
Example of a package.json file:
```
{
“name”: “my-app”,
“version”: “1.0.0”,
“description”: “A great app”,
“main”: “index.js”,
“scripts”: {
“start”: “node index.js“
},
“dependencies”: {
“express”: “^4.17.1”,
“mongoose”: “^5.10.11“
}
}
```
In this `package.json` example, the application has two dependencies: `express` and `mongoose`.
