# Learning Journal Node.js: import modules

# Questions

Hello! Welcome to my day-to-day learning of Node.js. :)

1. How do you import a 3rd party module into the JS file you're working with?
    
2. How do you import your own JS file into the file you're working with?
    

Does **require** syntax allow for named imports / exports, or does it need to be exported as a default that's then destructured?

## How do you import a 3rd party module?

The first step in importing a 3rd party module is to install it using **npm**.

If we're trying to load in `uuid`, for example, we would run the command:

```bash
npm install uuid
```

This adds the `uuid` module as a dependency to the project and loads the module source to the **node\_modules** folder in the project directory's root.

After the module source is loaded into the **node\_modules** directory, the process is the same as with using a native module. If, for example, you have a module called `uuid`, you would specify a variable to be used as a reference for the module:

```javascript
const uuid = require('uuid')

const id = uuid.v4()
console.log(id) // 61b702dd-5169-430b-9e73-dcebe914708e
```

If you need to reference a specific version number of the module, you can use the `@` syntax to lock down the version. For example:

```bash
npm install uuid@8.2.0
```

This will add an entry to **package.json**'s dependencies with `uuid` as the **property** with `^8.2.0` as the **value,** and the **TAR Archive file** reference is added to the **package-lock.json**.

```json
// package.json
{
  ...
  "dependencies": {
    "uuid": "^8.2.0"
  }
  ...
}
```

```json
// package-lock.json
{
  ...
    "node_modules/uuid": {
      "version": "8.2.0",
      "resolved": "https://registry.npmjs.org/uuid/-/uuid-8.2.0.tgz",
      "integrity": "sha512-CYpGiFTUrmI6OBMkAdjSDM0k5h8SkkiTP4WAjQgDgNB1S3Ou9VBEvr6q0Kv2H1mMk7IWfxYGpMH5sd5AvcIV2Q==",
      "bin": {
        "uuid": "dist/bin/uuid"
      }
    },
  ...
}
```

### Note on versioning

The package.json may contain a different version number for a given module than the **package-lock.json**. This can be the case when running `npm install` or when adding new modules to the project, and if the module's version number is not locked down. Generally, I've seen utility to allow for **fix versions** to flow into the project. It can, however, be problematic if minor versions are allowed to flow into the project and a significant bug is introduced as a result. This can be particularly troubling when you're only anticipating bugs to be introduced by your project rather than an open-source project's **module**.

## How do you import your own JS modules?

Each JS file has its own scope. So any variables you define, for example, in `app.js` are out of scope in `utils.js`\--even if you import utils.js into app.js. To bring a given reference into scope, the imported file must use the `module.exports` syntax. This is essentially a `default` export, that can then be referenced with the `require` syntax.

For example, if we try to import a single reference:

```javascript
// utils.js
const name = 'Nathan'

module.exports = name
```

```javascript
// app.js
const name = require('./utils.js')

console.log(name) // "Nathan"
```

The `name` reference defined in the `utils.js` file can now be used in the `app.js` file.

We can also use the `module.exports` syntax to export a mapped object, containing multiple references:

```javascript
// utils.js
const name = 'Nathan'
const add = (a, b) => {
  return a + b
}

module.exports = {
  name,
  add,
}
```

```javascript
// app.js
const utils = require('./utils.js')

console.log(utils.name) // "Nathan"
console.log(utils.add(3,2)) // 5
```

## Does **require** syntax allow for named imports / exports?

While it appears that require syntax does not allow for **named exports**, we can leverage ES6 **destructuring** syntax to pull out the individual references, and treat the `module.exports` it like a **named import**:

```javascript
// utils.js
const name = 'Nathan'
const add = (a, b) => {
  return a + b
}

module.exports = {
  name,
  add,
}
```

```javascript
// app.js
const { name, add } = require('./utils.js')

console.log(name) // "Nathan"
console.log(add(3,2)) // 5
```