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Reading JSON

Introduction

JSON (JavaScript Object Notation) is one of the most commonly used formats for storing and exchanging structured data. In Node.js applications, JSON files are frequently used to store configuration settings, application data, user information, and API responses.

Reading JSON files allows applications to load data into memory and work with it as JavaScript objects.

For automation engineers, reading JSON files is an essential skill because automation frameworks use JSON files to store test data, configuration settings, API request payloads, expected responses, and environment variables.

In this tutorial, you’ll learn multiple ways to read JSON files in Node.js.

Why Read JSON Files?

Reading JSON files allows applications to:

  • Load configuration files

  • Read application settings

  • Process user information

  • Import product data

  • Read API request payloads

  • Load automation test data

  • Perform data-driven testing

Sample JSON File

Suppose employee.json contains:

{
    "id": 101,
    "name": "John",
    "department": "IT",
    "salary": 65000
}

Method 1: Read JSON Using fs.readFile()

The most common method is using the built-in File System (fs) module.

const fs = require("fs");

fs.readFile(
    "employee.json",
    "utf8",
    (error, data) => {
        if (error) {
            console.log(error);
            return;
        }

        const employee = JSON.parse(data);

        console.log(employee);
    }
);

Sample Output

{
  id: 101,
  name: 'John',
  department: 'IT',
  salary: 65000
}

Understanding JSON.parse()

The readFile() method returns file contents as a string.

Use JSON.parse() to convert the JSON string into a JavaScript object.

const employee = JSON.parse(data);

Now individual properties can be accessed.

console.log(employee.name);

Sample Output

John

Method 2: Read JSON Using readFileSync()

const fs = require("fs");

const data = fs.readFileSync(
    "employee.json",
    "utf8"
);

const employee = JSON.parse(data);

console.log(employee.department);

Sample Output

IT

Method 3: Load JSON Using require()

Node.js can directly import JSON files.

const employee = require("./employee.json");

console.log(employee.salary);

Sample Output

65000

Note: require() caches the JSON file after the first load. If the file changes while the application is running, require() will continue returning the cached version unless the cache is cleared or the application is restarted.

Reading a JSON Array

Suppose employees.json contains:

[
    {
        "id": 1,
        "name": "John"
    },
    {
        "id": 2,
        "name": "Alice"
    },
    {
        "id": 3,
        "name": "Bob"
    }
]

const fs = require("fs");

fs.readFile(
    "employees.json",
    "utf8",
    (error, data) => {
        const employees = JSON.parse(data);

        console.log(employees);
    }
);

Sample Output

[
  { id: 1, name: 'John' },
  { id: 2, name: 'Alice' },
  { id: 3, name: 'Bob' }
]

Loop Through JSON Data

const fs = require("fs");

fs.readFile(
    "employees.json",
    "utf8",
    (error, data) => {

        const employees = JSON.parse(data);

        employees.forEach(employee => {
            console.log(employee.name);
        });

    }
);

Sample Output

John
Alice
Bob

Real-World Example

Read application configuration.

Suppose config.json contains:

{
    "browser": "chrome",
    "headless": true,
    "baseUrl": "https://example.com"
}

const config = require("./config.json");

console.log(config.browser);

console.log(config.baseUrl);

Sample Output

chrome
https://example.com

Automation Testing Example

Reading JSON files is widely used in automation frameworks.

Playwright Example

Load browser configuration.

const config = require("./playwright-config.json");

console.log(config.browser);

Selenium Example

Read login credentials.

const user = require("./user.json");

console.log(user.username);

Cypress Example

Read fixture data.

const product = require("./product.json");

console.log(product.productName);

API Testing Example

Read request payload.

const payload = require("./payload.json");

console.log(payload.email);

Data-Driven Testing Example

Read employee records.

const fs = require("fs");

const employees = JSON.parse(
    fs.readFileSync(
        "employees.json",
        "utf8"
    )
);

employees.forEach(employee => {
    console.log(employee.name);
});

Common Mistakes

Forgetting JSON.parse()

Incorrect:

console.log(data.name);

Since data is a string, this returns undefined.

Correct:

const employee = JSON.parse(data);

console.log(employee.name);

Invalid JSON Format

Incorrect JSON:

{
    "name": "John",
}

Trailing commas are not allowed.

Correct:

{
    "name": "John"
}

Forgetting Error Handling

Always check for file reading errors.

if (error) {
    console.log(error);
    return;
}

Best Practices

  • Prefer fs.readFile() for non-blocking operations.

  • Use JSON.parse() after reading JSON as text.

  • Use require() only for static JSON files that rarely change.

  • Validate JSON files before reading them.

  • Keep configuration and test data in separate JSON files.

  • Handle file reading errors properly.

  • Organize JSON files into dedicated folders such as config, data, or fixtures.

Conclusion

Reading JSON files is an essential skill for Node.js developers and automation engineers. Whether you’re loading configuration settings, reading test data, or processing API payloads, Node.js provides simple and efficient ways to work with JSON.

For automation engineers, JSON files simplify data-driven testing, configuration management, API validation, and environment setup.

Mastering JSON reading prepares you to build scalable Node.js applications and maintainable automation frameworks.

Frequently Asked Questions (FAQs)

Which module is used to read JSON files?

The built-in fs (File System) module.

Why is JSON.parse() required?

Because readFile() returns a string, JSON.parse() converts it into a JavaScript object.

Can I read JSON using require()?

Yes. Node.js allows direct importing of JSON files using require(), but the file is cached after the first load.

What is the difference between readFile() and readFileSync()?

  • readFile() is asynchronous and does not block execution.

  • readFileSync() is synchronous and blocks execution until the file has been read.

Why is reading JSON important in automation testing?

Automation engineers read JSON files to load configuration settings, test data, API request payloads, expected responses, and environment-specific information.

Key Takeaways

  • JSON files store structured data in a lightweight format.

  • Use the built-in fs module to read JSON files.

  • Use JSON.parse() to convert JSON strings into JavaScript objects.

  • readFile() performs asynchronous file reading.

  • readFileSync() performs synchronous file reading.

  • require() can directly import JSON files but caches the result.

  • Handle file reading and parsing errors properly.

  • JSON files are widely used in Playwright, Selenium, Cypress, API testing, and Node.js applications.

  • Store configuration and test data in dedicated JSON files.

  • Mastering JSON reading is essential for backend development and automation testing.