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JavaScript JSON - GeeksforGeeks

Last Updated : 11 Jul, 2025

JSON (JavaScript Object Notation) is a lightweight data format for storing and exchanging data. It is widely used to send data between a server and a client. JSON is simple, language-independent, and easy to understand.

• JSON stands for JavaScript Object Notation.
• It is a lightweight, text-based data interchange format.
• It is language-independent, meaning it can be used with most programming languages.
• JSON is derived from JavaScript but can be used with any programming language.
• JSON is "self-describing," making it human-readable.

Here is an example of JSON that defines an employee object containing an array of three employee records:

{
    "employees": [
        { "firstName": "Amit", "lastName": "Kumar" },
        { "firstName": "Jay", "lastName": "Sharma" },
        { "firstName": "Mohit", "lastName": "Patel" }
    ]
}

JSON syntax is derived from JavaScript objects. Here are the rules:

• Data is written as name/value pairs (e.g., "name": "Mohit").
• Objects are enclosed in curly braces {}.
• Arrays are enclosed in square brackets [].
• Strings are wrapped in double quotes.
• Data values can be strings, numbers, booleans, arrays, objects, or null.

You can use the JSON.parse() method to convert a JSON string into a JavaScript object.

const jsonStr = `{
    "emp": [
        { "firstName": "Amit", "lastName": "Kumar" },
        { "firstName": "Jay", "lastName": "Sharma" },
        { "firstName": "Mohit", "lastName": "Patel" }
    ]
}`;

const obj = JSON.parse(jsonStr);
console.log(obj.emp[1].firstName);

<p id="demo"></p>

<script>
    const s = `{
    "emp": [
        { "firstName": "Amit", "lastName": "Kumar" },
        { "firstName": "Jay", "lastName": "Sharma" },
        { "firstName": "Mohit", "lastName": "Patel" }
    ]
 }`;

    const obj = JSON.parse(s);
    document.getElementById("demo").innerHTML =
        obj.emp[1].firstName + " " + obj.emp[1].lastName;
</script>

To send data to a server, you need to convert a JavaScript object to a JSON string using JSON.stringify().

const obj = { fname: "Mohit", lname: "Kumar", age: 30 };
const jsonStr = JSON.stringify(obj);

console.log(jsonStr);

{"fname":"Mohit","lname":"Kumar","age":30}

JSON objects are collections of key/value pairs enclosed in curly braces {}.

{
    "fName": "Mohit",
    "lName": "Kumar",
    "age": 30
}

In JavaScript, you can access the data as follows:

const obj = { fName: "Mohit", lName: "Kumar", age: 30 };
console.log(obj.fName);

JSON arrays are collections of values enclosed in square brackets [].

{
    "hobbies": ["reading", "coding", "traveling"]
}

You can access the data in JavaScript like this:

const obj = { hobbies: ["reading", "coding", "traveling"] };
console.log(obj.hobbies[1]);

JSON is commonly used in APIs to exchange data between a client and server. In a typical web application, the server sends data to the client (frontend) as JSON.

Server Side:

• Data is stored as a JavaScript object.
• Before sending the data to the client, it's converted to a JSON string using JSON.stringify().

Client Side:

• The JSON string is received as part of an API response (e.g., via an HTTP GET request).
• The client parses this string back into a JavaScript object using JSON.parse().
• The parsed object is then used in the frontend code.

Here’s a JSON string received from the server

const jsonString = '{"name":"Mohit", "age":30}';

It has an object with the properties

• name: "Mohit"
• age: 30

To access its properties, we need to parse it into a JavaScript object:

const jsonS = '{"name":"Mohit", "age":30}';

const obj = JSON.parse(jsonS);
let name = obj.name;
let age = obj.age;

console.log(`Name: ${name}, Age: ${age}`);

Name: Mohit, Age: 30

• Easy to Use: Readable and easy to understand.
• Lightweight: Minimal overhead for data transmission.
• Cross-Language Support: Compatible with most programming languages.
• Built-In Methods in JavaScript: Simplifies parsing and stringifying.

• Always handle errors: When parsing JSON, always handle possible errors using try-catch blocks.
• Use JSON.stringify() carefully: When working with large objects, avoid stringifying large data structures unnecessarily, as it can be resource-intensive.
• Handle missing or extra properties: When receiving JSON from external sources, check for the existence of required properties before accessing them to avoid errors.

JSON is an essential data format in modern web development. Its simplicity and widespread support make it a great choice for exchanging data between a client and server. By understanding how to parse, manipulate, and stringify JSON in JavaScript, you can effectively handle data in web applications.

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