Suggest an edit

Improve this article

Refine the answer for “Object in JS”. 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)

**In short:**
An **object (Object)** in JavaScript is a **"key -> value" data structure**,
where keys are strings or symbols, and values can be **any data type** (including other objects and functions).

---

### Detailed explanation

Objects are the **main way to store and organize data** in JS.
They let you group related values into a single entity and access them by name (keys).

```javascript
const user = {
  name: 'Alice',
  age: 25,
  isAdmin: true
};
```

Here `user` is an object with three properties:
`name`, `age`, `isAdmin`.

---

### 1. Accessing properties

```javascript
console.log(user.name);    // "Alice"
console.log(user['age']);  // 25
```

You can access them via:

- **dot notation** (`obj.key`), when the name is known;
- **square brackets** (`obj['key']`), when the name is stored in a variable.

---

### 2. Adding and removing properties

```javascript
user.city = 'Kyiv';       // add a new one
delete user.isAdmin;      // remove
```

---

### 3. Iterating over an object's properties

```javascript
for (let key in user) {
  console.log(key, user[key]);
}
```

Prints:

```javascript
name Alice
age 25
city Kyiv
```

---

### 4. Nested objects

```javascript
const user = {
  name: 'Alice',
  address: {
    city: 'Kyiv',
    zip: '123456'
  }
};

console.log(user.address.city); // "Kyiv"
```

A property can contain **another object**,
which lets you build complex structures.

---

### 5. Object methods (functions as properties)

```javascript
const user = {
  name: 'Alice',
  sayHi() {
    console.log(`Hi, ${this.name}!`);
  }
};

user.sayHi(); // "Hi, Alice!"
```

A function inside an object is called a **method**.
`this` inside a method refers to the object itself (`user`).

---

### 6. Checking if a property exists

```javascript
console.log('name' in user); // true
console.log(user.hasOwnProperty('age')); // true
```

---

### 7. Copying objects

```javascript
const clone = { ...user };               // shallow copy (spread)
const deepClone = structuredClone(user); // deep copy
```

---

### 8. Objects can be created in different ways

```javascript
const obj1 = {};                  // object literal
const obj2 = new Object();        // via constructor
const obj3 = Object.create(null); // without a prototype
```

---

### Summary

| Property | Description |
|---|---|
| Type | Composite (reference type) |
| Stores | "Key -> value" pairs |
| Keys | Strings or symbols |
| Values | Any data type |
| Main operations | Adding, reading, removing, iterating |
| Often used for | Representing entities, settings, data |

Markdown · drag & drop images · ⌘B / ⌘I shortcuts391 words

For the reviewer

Note to the moderator (optional)

Visible only to the moderator. Helps review go faster.