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**`navigator` is a property of the `window` object that represents the Browser Object Model (BOM) and lets JavaScript interact with the browser and the device rather than with the page.** Through it you can learn the browser type and operating system (`userAgent`, `platform`, `vendor`), the interface language (`language`, `languages`), the network status (`onLine`), whether cookies are allowed (`cookieEnabled`), the number of logical cores (`hardwareConcurrency`) and the amount of memory (`deviceMemory`). It also exposes system capabilities: geolocation (`navigator.geolocation`), the clipboard (`navigator.clipboard`), the system share dialog (`navigator.share()`), vibration (`navigator.vibrate()`), camera and microphone (`navigator.mediaDevices`), Service Workers for PWAs and permission checks (`navigator.permissions`).

```javascript
console.log(window.navigator === navigator); // true
console.log(navigator.language); // "uk-UA"
console.log(navigator.onLine);   // true
```

**Key point:** `navigator` is the JavaScript window into the browser's characteristics and the device's system capabilities.

Shown above the full answer for quick recall.

Answer (EN)

**`navigator` is a property of the `window` object that represents the Browser Object Model (BOM), the interface through which JavaScript interacts with the browser rather than with the page.** Through it code learns the characteristics of the browser and the device and gains access to system capabilities: geolocation, the camera, the clipboard.

## Theory

### TL;DR
- `navigator` is an object inside `window`: `window.navigator === navigator` returns `true`.
- It represents the BOM, the model of the browser, not the model of the document.
- It gives information: browser type, OS, language, online status, cookies, cores, memory.
- It gives capabilities: geolocation, clipboard, share, vibration, camera and microphone, Service Workers.
- Many of its APIs require a user permission and a secure context (HTTPS).

### Quick example
```javascript
console.log(window.navigator === navigator); // true

console.log(navigator.userAgent);
console.log(navigator.language);
console.log(navigator.onLine);
```

This prints something like:

```text
"Mozilla/5.0 (Windows NT 10.0; Win64; x64)..."
"uk-UA"
true
```

### What `navigator` is
`navigator` is a property of the `window` object. It represents the Browser Object Model (BOM), the interface that lets JavaScript interact with the browser rather than with the page. Finding and changing elements is the job of `document`, while `navigator` is responsible for the environment in which that document is open.

```javascript
console.log(window.navigator === navigator); // true
```

### The main properties of `navigator`

| Property | What it does |
| --- | --- |
| `navigator.userAgent` | a string describing the browser and the OS |
| `navigator.language` | the user interface language (`"en-US"`, `"uk-UA"`) |
| `navigator.languages` | an array of preferred languages |
| `navigator.platform` | the platform or OS (`"Win32"`, `"MacIntel"`, `"Linux x86_64"`) |
| `navigator.onLine` | `true` if there is a network connection |
| `navigator.cookieEnabled` | `true` if cookies are allowed in the browser |
| `navigator.hardwareConcurrency` | the number of logical CPU cores |
| `navigator.deviceMemory` | the amount of device RAM (in GB) |
| `navigator.vendor` | the browser vendor (for example, `"Google Inc."`) |

### The methods of `navigator`

| Method | Description |
| --- | --- |
| `navigator.geolocation.getCurrentPosition()` | get the user's geolocation |
| `navigator.clipboard.writeText()` / `readText()` | work with the clipboard |
| `navigator.share()` | open the system share dialog (on mobile) |
| `navigator.vibrate()` | vibration on mobile devices |
| `navigator.mediaDevices.getUserMedia()` | access to the camera and microphone |
| `navigator.serviceWorker` | work with Service Workers (PWA, offline mode) |
| `navigator.permissions.query()` | check whether an API is allowed (for example, geolocation) |

### Usage examples

Check the browser:

```javascript
if (navigator.userAgent.includes("Chrome")) {
  console.log("The user is in Chrome");
}
```

Check the connection:

```javascript
if (!navigator.onLine) {
  alert("No internet connection!");
}
```

Get the current coordinates:

```javascript
navigator.geolocation.getCurrentPosition(pos => {
  console.log(pos.coords.latitude, pos.coords.longitude);
});
```

> This method asks the user for permission.

Copy text to the clipboard:

```javascript
navigator.clipboard.writeText("Hello, world!");
```

Get the user's language:

```javascript
console.log(`Your language: ${navigator.language}`);
```

### Structure and summary

| Question | Answer |
| --- | --- |
| What it does | Provides information about the browser and the device |
| Where it lives | Inside `window` (`window.navigator`) |
| What you can learn | browser type, language, OS, online status |
| What you can do | get geolocation, copy to the clipboard, call share, use the camera |
| Typical example | `navigator.userAgent`, `navigator.onLine`, `navigator.geolocation.getCurrentPosition()` |

So `navigator` is the object through which JavaScript learns the characteristics of the browser and the device and interacts with system capabilities: geolocation, the camera, the clipboard, PWAs and so on.

### Common mistakes
- Detecting the browser from `navigator.userAgent`. That string is easy to spoof and browsers deliberately mask it; checking for the capability itself (feature detection) is more reliable.
- Treating `navigator.onLine === true` as proof of internet access. It only means there is a network connection, not that the server responds.
- Using `navigator.platform`. The property is deprecated; the modern replacement is `navigator.userAgentData`.
- Calling `navigator.clipboard`, `geolocation` or `mediaDevices` over HTTP. These APIs only work in a secure context (HTTPS or `localhost`).
- Forgetting to handle the user denying permission: `getCurrentPosition()` takes a second callback for errors, and without it the code silently does nothing.
- Expecting `deviceMemory` and `hardwareConcurrency` to exist everywhere. They are not supported in every browser and return rounded values.

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