Node.js JSON Practice Questions with Solutions

Introduction

JSON, or JavaScript Object Notation, is one of the most common data formats used in Node.js applications and APIs. It is used to store and exchange structured data between a server and a client. In this chapter, you will practice creating JSON objects, converting JavaScript objects to JSON, parsing JSON strings, sending JSON responses, reading JSON data, updating JSON data, and handling JSON errors with simple step-by-step examples. Node.js JSON practice questions with solutions help to build concepts.

Question 1: How do you create a JSON object in Node.js?

Problem

Create a student object containing a name, age, and course, and display the data.

Solution

const student = {
    name: "Riya",
    age: 18,
    course: "Node.js"
};

console.log(student);
console.log(student.name);
console.log(student.course);

Output

{
  name: 'Riya',
  age: 18,
  course: 'Node.js'
}

Riya
Node.js

Step-by-Step Explanation

Create an object using {}.
Add properties such as name, age, and course.
Use dot notation to access individual values.
student.name returns the student’s name.
student.course returns the course name.

Important Point

A JavaScript object and a JSON string are not exactly the same thing. JSON is a text-based data format used for storing and exchanging data.

Question 2: How do you convert a JavaScript object into JSON?

Problem

Convert a JavaScript object into a JSON string using JSON.stringify().

Solution

const student = {
    name: "Aman",
    age: 19,
    course: "JavaScript"
};

const jsonData = JSON.stringify(student);

console.log(jsonData);
console.log(typeof jsonData);

Output

{"name":"Aman","age":19,"course":"JavaScript"}

string

Step-by-Step Explanation

Create a JavaScript object.
Store it inside student.
Use JSON.stringify().
The object is converted into a JSON string.
typeof confirms that the result is a string.

Important Point

Use:

JSON.stringify(object);

when you need to convert a JavaScript object into JSON text.

Question 3: How do you convert JSON into a JavaScript object?

Problem

Convert a JSON string into a JavaScript object using JSON.parse().

Solution

const jsonData = `
{
    "name": "Riya",
    "age": 18,
    "course": "Node.js"
}
`;

const student = JSON.parse(jsonData);

console.log(student);
console.log(student.name);
console.log(student.course);

Output

{
  name: 'Riya',
  age: 18,
  course: 'Node.js'
}

Riya
Node.js

Step-by-Step Explanation

Store JSON data inside a string.
Use JSON.parse().
The JSON string becomes a JavaScript object.
Access its properties using dot notation.

The basic syntax is:

const object = JSON.parse(jsonString);

Question 4: How do you send JSON from a Node.js server?

Problem

Create a Node.js server that sends student information as a JSON response.

Solution

const http = require("http");

const server = http.createServer((req, res) => {

    const student = {
        name: "Riya",
        age: 18,
        course: "Node.js"
    };

    res.writeHead(200, {
        "Content-Type": "application/json"
    });

    res.end(JSON.stringify(student));
});

server.listen(3000, () => {
    console.log(
        "Server running at http://localhost:3000"
    );
});

Output

Open:

http://localhost:3000

You will receive:

{
    "name": "Riya",
    "age": 18,
    "course": "Node.js"
}

Step-by-Step Explanation

Create a Node.js HTTP server.
Create a JavaScript object.
Set the response content type to application/json.
Convert the object into a JSON string.
Send it using res.end().

Important Point

When sending JSON from a server, use:

"Content-Type": "application/json"

This tells the client that the response contains JSON data.

Question 5: How do you work with a JSON array?

Problem

Create a JSON-compatible array containing information about three students.

Solution

const students = [
    {
        name: "Riya",
        age: 18
    },
    {
        name: "Aman",
        age: 19
    },
    {
        name: "Neha",
        age: 17
    }
];

console.log(students);
console.log(students[0].name);
console.log(students[1].age);

Output

[
  { name: 'Riya', age: 18 },
  { name: 'Aman', age: 19 },
  { name: 'Neha', age: 17 }
]

Riya
19

Step-by-Step Explanation

Create an array using [].
Add multiple objects to the array.
Each object represents one student.
Use an index to access a student.
Use a property name to access specific information.

For example:

students[0].name

returns:

Riya

Question 6: How do you convert a JSON array into a JavaScript array?

Problem

Convert a JSON string containing multiple students into a JavaScript array and display each student’s name.

Solution

const jsonData = `
[
    {
        "name": "Riya",
        "age": 18
    },
    {
        "name": "Aman",
        "age": 19
    },
    {
        "name": "Neha",
        "age": 17
    }
]
`;

const students = JSON.parse(jsonData);

students.forEach((student) => {
    console.log(student.name);
});

Output

Riya
Aman
Neha

Step-by-Step Explanation

Store the JSON array inside a string.
Use JSON.parse().
JSON becomes a JavaScript array.
Use forEach() to loop through the students.
Display each student’s name.

Important Point

JSON.parse() can convert a valid JSON array string into a JavaScript array.

Question 7: How do you update JSON data in Node.js?

Problem

Create a student object and change the student’s age from 18 to 19.

Solution

const student = {
    name: "Riya",
    age: 18,
    course: "Node.js"
};

console.log("Before update:");
console.log(student);

student.age = 19;

console.log("After update:");
console.log(student);

Output

Before update:
{
  name: 'Riya',
  age: 18,
  course: 'Node.js'
}

After update:
{
  name: 'Riya',
  age: 19,
  course: 'Node.js'
}

Step-by-Step Explanation

Create the student object.
Access the age property.
Assign a new value.
The age changes from 18 to 19.

The important line is:

student.age = 19;

Important Point

If your data is currently a JSON string, first convert it into a JavaScript object using JSON.parse() before updating it.

Question 8: How do you safely handle invalid JSON?

Problem

Try to parse invalid JSON without crashing the Node.js application.

Solution

const jsonData = `
{
    "name": "Riya",
    "age": 18,
}
`;

try {

    const student = JSON.parse(jsonData);

    console.log(student);

} catch (error) {

    console.log("Invalid JSON data.");
}

Output

Invalid JSON data.

Step-by-Step Explanation

Store the JSON string.
Notice that the JSON contains an error.
JSON.parse() can throw an error for invalid JSON.
Put the parsing operation inside try.
Handle the error inside catch.
The application can continue running instead of stopping unexpectedly.

Important Point

Valid JSON does not allow a trailing comma:

{
    "name": "Riya",
    "age": 18
}

This is invalid:

{
    "name": "Riya",
    "age": 18,
}

Question 9: How do you send a JSON array through a Node.js API?

Problem

Create an API route /api/students that returns a list of students as JSON.

Solution

const http = require("http");

const students = [
    {
        id: 1,
        name: "Riya",
        course: "Node.js"
    },
    {
        id: 2,
        name: "Aman",
        course: "JavaScript"
    },
    {
        id: 3,
        name: "Neha",
        course: "Python"
    }
];

const server = http.createServer((req, res) => {

    if (req.url === "/api/students") {

        res.writeHead(200, {
            "Content-Type": "application/json"
        });

        res.end(
            JSON.stringify(students)
        );

    } else {

        res.writeHead(404, {
            "Content-Type": "application/json"
        });

        res.end(
            JSON.stringify({
                error: "Route not found"
            })
        );
    }
});

server.listen(3000, () => {
    console.log(
        "API running at http://localhost:3000"
    );
});

Output

Open:

http://localhost:3000/api/students

Response:

[
    {
        "id": 1,
        "name": "Riya",
        "course": "Node.js"
    },
    {
        "id": 2,
        "name": "Aman",
        "course": "JavaScript"
    },
    {
        "id": 3,
        "name": "Neha",
        "course": "Python"
    }
]

Step-by-Step Explanation

Create an array of student objects.
Create an HTTP server.
Check the requested URL.
Match /api/students.
Set the response content type to JSON.
Convert the array into a JSON string.
Send the JSON response.
Return a JSON error when the route does not exist.

Question 10: How do you build a complete JSON API in Node.js?

Problem

Create a small JSON API with:

/api/student
/api/courses
/api/status
JSON responses
404 JSON error handling

Solution

const http = require("http");

const server = http.createServer((req, res) => {

    res.setHeader(
        "Content-Type",
        "application/json"
    );

    if (req.method !== "GET") {

        res.writeHead(405);

        res.end(JSON.stringify({
            error: "Method Not Allowed"
        }));

        return;
    }

    if (req.url === "/api/student") {

        const student = {
            id: 1,
            name: "Riya",
            age: 18,
            course: "Node.js"
        };

        res.writeHead(200);

        res.end(
            JSON.stringify(student)
        );

    } else if (req.url === "/api/courses") {

        const courses = [
            "JavaScript",
            "Node.js",
            "Python",
            "SQL"
        ];

        res.writeHead(200);

        res.end(
            JSON.stringify(courses)
        );

    } else if (req.url === "/api/status") {

        const status = {
            success: true,
            message: "API is working"
        };

        res.writeHead(200);

        res.end(
            JSON.stringify(status)
        );

    } else {

        res.writeHead(404);

        res.end(JSON.stringify({
            error: "API route not found"
        }));
    }
});

server.listen(3000, () => {
    console.log(
        "JSON API running at http://localhost:3000"
    );
});

Output

Student API

Open:

http://localhost:3000/api/student

Response:

{
    "id": 1,
    "name": "Riya",
    "age": 18,
    "course": "Node.js"
}

Courses API

Open:

http://localhost:3000/api/courses

Response:

[
    "JavaScript",
    "Node.js",
    "Python",
    "SQL"
]

Status API

Open:

http://localhost:3000/api/status

Response:

{
    "success": true,
    "message": "API is working"
}

Unknown API

Open:

http://localhost:3000/api/test

Response:

{
    "error": "API route not found"
}

Step-by-Step Explanation

Import the http module.
Create the HTTP server.
Set the response content type to JSON.
Check the HTTP method.
Create the /api/student route.
Create the /api/courses route.
Create the /api/status route.
Convert JavaScript objects and arrays into JSON using JSON.stringify().
Send each response with res.end().
Return status 404 for an unknown API route.
Return status 405 for unsupported HTTP methods.
Start the server on port 3000.

This is a simple example of how JSON is commonly used when building Node.js APIs.

Key Takeaways

JSON stands for JavaScript Object Notation.
JSON is commonly used to exchange data between clients and servers.
JavaScript objects and JSON strings are different.
JSON.stringify() converts JavaScript data into a JSON string.
JSON.parse() converts valid JSON into JavaScript data.
JSON can contain objects and arrays.
JSON property names are written using double quotes.
JSON does not allow trailing commas.
Node.js APIs commonly return JSON responses.
Use Content-Type: application/json for JSON responses.
JSON.stringify() is commonly used before sending API data.
JSON.parse() is useful when receiving JSON text.
try...catch can be used to handle invalid JSON.
JSON arrays are useful for representing lists of data.
JSON objects are useful for representing structured information.
APIs frequently use JSON for communication between frontend and backend applications.

FAQs

1. What is JSON in Node.js?

JSON is a text-based data format commonly used to store and exchange structured information.

For example:

{
    "name": "Riya",
    "age": 18
}

Node.js applications frequently use JSON when communicating with APIs and databases.

2. What is the difference between JSON and a JavaScript object?

A JavaScript object is a data structure used directly by JavaScript.

const student = {
    name: "Riya",
    age: 18
};

JSON is a text format:

{
    "name": "Riya",
    "age": 18
}

Use JSON.stringify() to convert an object into JSON text and JSON.parse() to convert JSON text into a JavaScript value.

3. What does `JSON.stringify()` do in Node.js?

JSON.stringify() converts a JavaScript object or array into a JSON string.

Example:

const student = {
    name: "Riya",
    age: 18
};

const jsonData = JSON.stringify(student);

console.log(jsonData);

Output:

{"name":"Riya","age":18}

4. What does `JSON.parse()` do?

JSON.parse() converts a valid JSON string into a JavaScript object or array.

Example:

const data = '{"name":"Riya","age":18}';

const student = JSON.parse(data);

console.log(student.name);

Output:

Riya

5. How do I send JSON from a Node.js server?

Set the content type to JSON and use JSON.stringify():

res.writeHead(200, {
    "Content-Type": "application/json"
});

res.end(JSON.stringify(data));

This tells the client that the response contains JSON.

6. What happens if `JSON.parse()` receives invalid JSON?

JSON.parse() throws an error when the supplied string is not valid JSON.

You can handle it using try...catch:

try {
    const data = JSON.parse(jsonData);
} catch (error) {
    console.log("Invalid JSON");
}

7. Why is JSON important in Node.js?

JSON is important because Node.js applications frequently communicate with web browsers, frontend applications, REST APIs, and other services.

It provides a simple and widely supported format for exchanging structured data between different systems.

Written by Shubhranshu Shekhar, who has trained 20000+ students in coding.

Rishabh Kumar

Introduction

Question 1: How do you create a JSON object in Node.js?

Problem

Solution

Output

Step-by-Step Explanation

Important Point

Question 2: How do you convert a JavaScript object into JSON?

Problem

Solution

Output

Step-by-Step Explanation

Important Point

Question 3: How do you convert JSON into a JavaScript object?

Problem

Solution

Output

Step-by-Step Explanation

Question 4: How do you send JSON from a Node.js server?

Problem

Solution

Output

Step-by-Step Explanation

Important Point

Question 5: How do you work with a JSON array?

Problem

Solution

Output

Step-by-Step Explanation

Question 6: How do you convert a JSON array into a JavaScript array?

Problem

Solution

Output

Step-by-Step Explanation

Important Point

Question 7: How do you update JSON data in Node.js?

Problem

Solution

Output

Step-by-Step Explanation

Important Point

Question 8: How do you safely handle invalid JSON?

Problem

Solution

Output

Step-by-Step Explanation

Important Point

Question 9: How do you send a JSON array through a Node.js API?

Problem

Solution

Output

Step-by-Step Explanation

Question 10: How do you build a complete JSON API in Node.js?

Problem

Solution

Output

Student API

Courses API

Status API

Unknown API

Step-by-Step Explanation

Key Takeaways

FAQs

1. What is JSON in Node.js?

2. What is the difference between JSON and a JavaScript object?

3. What does JSON.stringify() do in Node.js?

4. What does JSON.parse() do?

5. How do I send JSON from a Node.js server?

6. What happens if JSON.parse() receives invalid JSON?

7. Why is JSON important in Node.js?

Related Posts

3. What does `JSON.stringify()` do in Node.js?

4. What does `JSON.parse()` do?

6. What happens if `JSON.parse()` receives invalid JSON?