Suggest an edit

Improve this article

Refine the answer for “What is JSON?”. 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)

**JSON** is one of the most important concepts in frontend and web development in general.
Simply put:

> **JSON (JavaScript Object Notation)** is a **text format for storing and exchanging data**,
> understandable to both humans and computers.

---

## Example of JSON

```javascript
{
  "name": "Oleh",
  "age": 25,
  "isAdmin": false,
  "skills": ["JavaScript", "React", "Node.js"],
  "address": {
    "city": "Kyiv",
    "zip": 123456
  }
}
```

> This is a regular JSON document.
> Essentially it is a **string** that holds structured data.
> Such data is easy to read and transmit over the network.

---

## Where JSON is used

1. **Exchanging data between the client and the server**
The server sends JSON, the browser reads it:

```javascript
  fetch('/api/user')
    .then(res => res.json())
    .then(data => console.log(data.name));
  ```
2. **Storing data in localStorage**

```javascript
  const user = { name: 'Oleh', age: 25 };
  localStorage.setItem('user', JSON.stringify(user));
  ```
3. **Settings and configuration**
(for example, `package.json` in Node.js projects):

```javascript
  {
    "name": "my-project",
    "version": "1.0.0",
    "scripts": {
      "start": "node index.js"
    }
  }
  ```

---

## JSON syntax rules

| Rule | Description |
|---|---|
| Keys are **always in double quotes** | `"name": "Oleh"` |
| Strings are also **in double quotes** | `"city": "Kyiv"` |
| Only simple types are supported | `string`, `number`, `boolean`, `null`, `object`, `array` |
| No functions | `function() {}` → error |
| No `undefined` and `Symbol` | they are ignored |
| Comma between elements | but **not** after the last element |

---

## Basic JSON data types

| Type | Example |
|---|---|
| **string** | `"Oleh"` |
| **number** | `25` |
| **boolean** | `true`, `false` |
| **null** | `null` |
| **object** | `{ "a": 1, "b": 2 }` |
| **array** | `[1, 2, 3]` |

---

## Difference between JSON and JavaScript objects

| Feature | JSON | JavaScript object |
|---|---|---|
| Keys | Only in `"double quotes"` | Can be without quotes |
| Strings | Only `"double"` | `'single'` or `"double"` |
| Types | Only simple ones (`string`, `number`, etc.) | Any (`function`, `undefined`, `symbol`) |
| Purpose | Storing/exchanging data | Working with data in JS code |

---

## Converting between an object and JSON

```javascript
const obj = { name: 'Oleh', age: 25 };

// object -> JSON
const json = JSON.stringify(obj);
console.log(json);
// '{"name":"Oleh","age":25}'

// JSON -> object
const parsed = JSON.parse(json);
console.log(parsed.name); // 'Oleh'
```

---

## Summary

| Parameter | JSON |
|---|---|
| Full name | JavaScript Object Notation |
| Format | Text |
| Used for | Storing and exchanging data |
| Typical operations | `JSON.stringify()` and `JSON.parse()` |
| Based on | JavaScript syntax |
| Supported | In all languages (Python, Java, C#, Go, etc.) |

---

## In short

> **JSON** is a *universal data format*
> that lets you transmit complex structures (objects, arrays and so on)
> as a plain text string.

Markdown · drag & drop images · ⌘B / ⌘I shortcuts491 words

For the reviewer

Note to the moderator (optional)

Visible only to the moderator. Helps review go faster.