Suggest an edit

Improve this article

Refine the answer for “What is scope (variable visibility)?”. Your changes go to moderation before they’re published.

Approval required

Content

What you’re changing

Title (EN)

Short answer (EN)

Shown above the full answer for quick recall.

Answer (EN)

**Scope** is a mechanism in JavaScript that determines **where in the code variables and functions are accessible** (that is, in which parts of the program they can be referenced).

---

### Main types of scope

#### 1. **Global Scope**

Variables declared outside functions or blocks are accessible **everywhere** in the code.

```javascript
let name = 'Tim'; // global variable

function greet() {
  console.log('Hello, ' + name); // accessible here
}

greet(); // Hello, Tim
console.log(name); // also accessible here
```

---

#### 2. **Function Scope**

Variables declared with `var`, `let`, or `const` **inside a function** are accessible **only inside that function**.

```javascript
function example() {
  let message = 'Inside function';
  console.log(message); // works
}

example();
console.log(message); // Error: message is not defined
```

---

#### 3. **Block Scope**

Variables declared with `let` or `const` **inside a block** `{ }` are accessible only **inside that block**.

```javascript
if (true) {
  const x = 10;
  let y = 20;
  var z = 30; // var has no block scope
}

console.log(z); // 30 (var is visible outside the block)
console.log(x); // Error
console.log(y); // Error
```

---

#### 4. **Lexical Scope**

JavaScript uses **lexical (static) scope** - this means that access to variables is determined by **where functions are located in the code**, not by where they are called.

```javascript
function outer() {
  const outerVar = 'I am outside';

function inner() {
    console.log(outerVar); // has access to outerVar
  }

return inner;
}

const fn = outer();
fn(); // "I am outside"
```

> Here, `inner` remembered the environment in which it was created - this is exactly what a closure is.

---

### Summary

| Scope type | Where it is created | Accessibility |
|---|---|---|
| **Global** | Outside functions and blocks | Everywhere |
| **Function** | Inside a function | Only inside that function |
| **Block** | Inside `{ }` (if, for, etc.) | Only within the block |
| **Lexical** | At the time the code is written | Access to variables from outer scopes |

Markdown · drag & drop images · ⌘B / ⌘I shortcuts339 words

For the reviewer

Note to the moderator (optional)

Visible only to the moderator. Helps review go faster.