Testing JSON Formatter Browser Extensions

JSON (JavaScript Object Notation) is the de facto standard for data interchange on the web. As developers frequently work with JSON data, especially when interacting with APIs, browser extensions that format and display raw JSON in a readable structure are incredibly useful. However, like any software, these extensions need to be reliable. This article explores various aspects of testing JSON formatter browser extensions to ensure they are accurate, performant, and secure.

Why Testing Is Crucial

While a JSON formatter might seem simple, its functionality can impact a developer's workflow significantly. Untested or poorly tested extensions can lead to:

• Incorrect Formatting: Displaying invalid JSON as valid, or valid JSON incorrectly.
• Performance Issues: Crashing or slowing down the browser when handling large or complex JSON.
• Security Risks: Potentially exposing sensitive data or being vulnerable to injection attacks (though less common for pure formatters, processing untrusted input always carries risks).
• Compatibility Problems: Failing to work correctly on certain websites, with specific JSON structures, or in different browser versions.

Comprehensive testing helps ensure the extension provides a consistent, reliable, and safe experience.

Key Areas to Test

When testing a JSON formatter extension, consider these key areas:

Formatting Accuracy

This is the core function. The extension must correctly parse and format various types of JSON.

• Valid JSON: Test with standard objects, arrays, nested structures, strings (with special characters, escaped quotes, Unicode), numbers (integers, floats, exponents, large numbers), booleans (true, false), and null.
• Edge Cases: Test with empty objects ({}), empty arrays ([]), JSON with whitespace variations, JSON where strings contain JSON-like syntax, very long strings.
• Invalid JSON: Test with deliberately malformed JSON (trailing commas, missing commas, unquoted keys, single quotes, comments, incorrect nesting). The extension should ideally display an error or the raw text clearly indicating it's not valid JSON.
• Different Encodings: Ensure it handles JSON served with different character encodings, particularly UTF-8.

Test by visiting URLs that serve various types of JSON responses or by pasting JSON directly into the extension's input area (if it has one). Compare the output to a known good formatter or online validator.

Performance

Formatting large JSON responses can be resource-intensive.

• Large Files: Test with JSON files ranging from a few MB up to tens or hundreds of MBs. Observe browser memory usage and CPU load. The extension should ideally handle reasonably large files without freezing the tab or the entire browser.
• Deeply Nested Structures: Test with JSON that has many levels of nesting.
• Long Arrays/Objects: Test with JSON containing objects with thousands of keys or arrays with thousands of elements.

Monitor browser task manager or developer tools (Performance tab) while formatting large JSON payloads.

Security

Since the extension processes data from potentially untrusted websites, security is paramount.

• XSS (Cross-Site Scripting): If the extension renders the JSON within the page or its own iframe/popup, ensure it properly sanitizes string values to prevent malicious HTML/JavaScript injection. For example, a string value like "<script>alert('XSS')</script>" should be displayed as text, not executed.
• JSON Hijacking: Older JSON APIs might return arrays or objects at the top level without protection against JSON hijacking. If the sensitive data was returned as a simple JSON array (e.g., [{...}, {...}]), this response was also a valid JavaScript array literal. In some scenarios (especially pre-ES5 browsers or specific execution contexts like overriding Array constructors), the malicious page could potentially read the values of this array. Similarly, if it was a simple object literal ({...}), it could potentially be assigned to a variable if the response was wrapped in parentheses. While modern APIs usually wrap responses in an object (e.g., {"data": [...]}) or use anti-hijacking prefixes, the extension should handle such potentially vulnerable formats safely, perhaps by only formatting responses with the correct Content-Type: application/json header, or by not running on arbitrary origins.
• Permissions: Review the permissions the extension requests. Does it need access to all websites (<all_urls>)? Does it justify those permissions based on its functionality? More permissions mean a larger attack surface if the extension is compromised.

Create test JSON payloads containing known XSS vectors within string values. Observe if the extension executes them. Understand how the extension obtains and renders the JSON data.

Compatibility

Extensions should work across different environments and scenarios.

• Browsers: Test on different major browsers where the extension is available ( Chrome, Firefox, Edge, etc.).
• Websites: Test on various websites that serve JSON, including those with complex headers, different content types (ensure it only activates for application/json or similar), and different security policies (CSP - Content Security Policy).
• Browser Versions: Test on the minimum supported browser version and the latest version.

Feature Testing

Most formatters offer additional features beyond basic formatting.

• Syntax Highlighting: Check if different JSON types (strings, numbers, booleans, null, keys, punctuation) are correctly highlighted.
• Collapsing/Expanding: Test collapsing and expanding objects and arrays at different levels of nesting. Ensure expand/collapse state is maintained correctly.
• Search/Filtering: If a search feature exists, test searching for keys, values, numbers, special characters, and phrases within strings. Test case sensitivity and highlighting of results.
• Copy Functionality: Test copying parts of the JSON tree or the entire formatted/raw JSON.
• Settings/Options: If the extension has settings (e.g., theme, indent size, line wrapping), test that they are applied correctly and persist.
• Raw/Formatted View Toggle: Ensure seamless switching between the original raw JSON and the formatted view.

User Interface and Experience

While not strictly functional testing, a good UX is vital for a developer tool.

• Readability: Is the formatted output easy to read? Is the theme contrast sufficient?
• Responsiveness: Does the interface scale well with different browser window sizes?
• Error Messages: If invalid JSON is detected, is the error message clear and helpful? Does it indicate the location of the error?
• Intuitiveness: Are features easy to find and use?

Creating Test Cases

You can create a suite of JSON test files covering the scenarios above.

// Valid JSON - Basic
{
  "name": "Test User",
  "age": 30,
  "isStudent": false,
  "courses": ["Math", "Science"],
  "address": {
    "street": "123 Main St",
    "city": "Anytown"
  },
  "contact": null
}

// Valid JSON - Edge Cases
{
  "emptyObject": {},
  "emptyArray": [],
  "longString": "This is a very long string with \"quotes\", newlines\n, and tabs\t.",
  "numberEdges": {
    "zero": 0,
    "float": 123.45,
    "exponent": 1.2e+5,
    "negative": -100,
    "large": 98765432101234567890
  },
  "unicode": "你好世界🌍", // Hello world emoji
  "whitespace": {"key":"value"} // Test different whitespace handling
}

// Invalid JSON - Trailing comma
{
  "item1": 1,
  "item2": 2, // Trailing comma here
}

// Invalid JSON - Unquoted key
{
  unquotedKey: "value"
}

// Invalid JSON - Single quotes
{
  "key": 'value'
}

// Invalid JSON - With comments (JSON doesn't support comments)
{
  // This is a comment
  "key": "value"
}

// Security - XSS Test (within a string value)
{
  "description": "This has <script>alert('XSS Vulnerability')</script> injected."
}

// Security - Potential JSON Hijacking Example (if fetched cross-origin without protection)
// This is an array at the root, which could be vulnerable in older contexts.
[
  {"id": 1, "data": "sensitive"},
  {"id": 2, "data": "more sensitive"}
]

Manual vs. Automated Testing

• Manual Testing: This is essential for verifying UX, visual formatting, and simple accuracy checks. A human eye is good at spotting subtle rendering issues or awkward interfaces.
• Automated Testing: For complex scenarios like parsing accuracy with many variations, performance under load, and basic security checks (like XSS vector rendering), automation is more efficient. This might involve using browser automation frameworks (like Puppeteer or Selenium, though integrating with extensions can be tricky) to load pages with specific JSON or inject JSON into test environments and verify the rendered output against expected results (e.g., by inspecting the generated HTML or using JavaScript within the page context). Running linters and vulnerability scanners against the extension's source code ( if open source) is also a form of automated testing.

Conclusion

JSON formatter browser extensions are valuable tools, but their reliability depends on thorough testing. By focusing on formatting accuracy across various JSON types and structures, evaluating performance with large datasets, diligently testing for security vulnerabilities (especially XSS and safe handling of responses), checking compatibility across browsers and websites, and ensuring features function correctly, developers can build or choose extensions they can trust. A systematic approach to testing, using a combination of manual checks and automated test cases, is key to delivering a high-quality and secure tool for the developer community.