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### What the `boolean` type does in TypeScript

The `boolean` type in TypeScript represents a **logical value** that can be **only one of two**:
`true` or `false`.

It is used to express logical states, for example "on / off", "active / inactive", "logged in / not", and so on.

---

### How to declare a variable of type `boolean`

#### 1. Explicit type annotation

```javascript
let isOnline: boolean = true;
let hasAccess: boolean = false;
```

#### 2. Implicit determination (type inference)

TypeScript automatically infers the type:

```javascript
let isActive = true; // type: boolean
```

---

### Usage examples

```javascript
let isAdmin: boolean = true;
let isLoggedIn: boolean = false;

// Use in conditions:
if (isAdmin) {
  console.log("Welcome, administrator!");
} else {
  console.log("Access restricted.");
}

// Assignment based on an expression:
let hasPermission: boolean = 5 > 2; // true
```

---

### Conversion to `boolean`

TypeScript (and JavaScript) automatically coerces values to a logical type in conditions.
Here are examples of which values are considered **falsy** and **truthy**:

| **Falsy** values (coerce to `false`) | **Truthy** values (coerce to `true`) |
|---|---|
| `false` | `true` |
| `0`, `-0` | Any nonzero number |
| `""` (empty string) | `"text"` |
| `null` | `{}`, `[]` |
| `undefined` | Any non-empty value |
| `NaN` |  |

Example:

```javascript
let value = "";
let isEmpty = Boolean(value); // false
```

---

### Important

- Use `boolean`, not the `Boolean` object:

```javascript
  let flag: boolean = true; // primitive
  let badFlag: Boolean = new Boolean(true); // object, not recommended
  ```
The `Boolean` object is always considered truthy, even if it wraps `false`:

```javascript
  if (new Boolean(false)) {
    console.log("This will run!");
  }
  ```

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