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## What the global object is

The **global object** is a special object that always exists, **regardless of the environment** (browser, Node.js, and so on). It represents the **global scope**, where all global variables and functions live.

Simply put:

> The global object is a "container" that holds all the variables and functions declared outside functions and modules.

---

## Examples of global objects in different environments

| Environment | Global object |
|---|---|
| **Browser** | `window` or `self` |
| **Web Worker** | `self` |
| **Node.js** | `global` |
| **Modern universal way** | `globalThis` |

---

## Example: browser

```javascript
var x = 10;

console.log(window.x); // 10
console.log(this.x);   // 10 (in the global scope)
```

The variable `x`, declared with `var`, automatically becomes a property of the global object `window`.

---

## Example: Node.js

```javascript
var y = 5;

console.log(global.y); // undefined
```

In Node.js, `var`, `let`, and `const` variables are **not added** to `global`, because Node.js uses a module system (each file is a separate module, not a global script).

---

## The universal way: globalThis

ES2020 introduced a new standard, `globalThis`, which works the same way **in every environment**.

```javascript
console.log(globalThis);
```

It works:

- in the browser -> `window`
- in Node.js -> `global`
- in a web worker -> `self`

---

## Relationship to the execution context

When the **global execution context** is created, the JS engine:

1. creates the **global object**;
2. sets `this` as a **reference to that object** (unless `strict mode` is used);
3. places all global declarations (`var`, `function`) into it.

Example:

```javascript
var a = 42;

function sayHi() {
  console.log("Hi");
}

console.log(globalThis.a); // 42
globalThis.sayHi();        // "Hi"
```

---

## The difference between let/const and var

Variables declared with `let` and `const`:

- **do not become properties of the global object**,
- but still exist in the **global scope**.

Example:

```javascript
let a = 10;
var b = 20;

console.log(window.a); // undefined
console.log(window.b); // 20
```

---

## Summary

| Feature | Description |
|---|---|
| What it is | The top-level object that always exists |
| Where it lives | In the global execution context |
| Automatically contains | Global functions (`setTimeout`, `fetch`, `console`, ...) |
| How to access it | `window` (browser), `global` (Node.js), `globalThis` (universal) |
| Specifics of `let`/`const` | They do not become properties of the global object |

---

## Practical example using globalThis

```javascript
globalThis.appName = "DemoApp";

function printName() {
  console.log(globalThis.appName);
}

printName(); // "DemoApp"
```

Works in the browser, in Node.js, and in any environment.

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