swagger-jsdoc setup in Express - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What does this swagger-jsdoc setup output?

Given this Express app setup with swagger-jsdoc, what will the /api-docs.json endpoint return?

Express

import express from 'express';
import swaggerJSDoc from 'swagger-jsdoc';

const app = express();

const options = {
  definition: {
    openapi: '3.0.0',
    info: {
      title: 'Sample API',
      version: '1.0.0'
    }
  },
  apis: ['./routes/*.js']
};

const swaggerSpec = swaggerJSDoc(options);

app.get('/api-docs.json', (req, res) => {
  res.json(swaggerSpec);
});

app.listen(3000);

A An HTML page showing API documentation

B A plain text string describing the API routes

C A JSON object with OpenAPI info and paths from './routes/*.js' files

D An error because './routes/*.js' files are missing

💡 Hint

swagger-jsdoc generates a JSON spec from options and comments in specified files.

The swaggerJSDoc function reads the options and extracts API documentation from the specified files. It returns a JSON object following the OpenAPI format. The endpoint /api-docs.json sends this JSON as response.

📝 Syntax

intermediate

Which option correctly initializes swagger-jsdoc?

Choose the correct way to initialize swagger-jsdoc with OpenAPI 3.0 and info title 'My API'.

A swaggerJSDoc({ openapi: '3.0.0', info: { title: 'My API' }, apis: ['./api.js'] })

B swaggerJSDoc({ openapi: '3.0.0', apis: ['./api.js'] })

C swaggerJSDoc({ info: { title: 'My API' }, apis: ['./api.js'] })

D swaggerJSDoc({ definition: { openapi: '3.0.0', info: { title: 'My API' } }, apis: ['./api.js'] })

💡 Hint

The OpenAPI info must be inside a 'definition' object.

The swagger-jsdoc options require a definition key containing the OpenAPI version and info. Options A, C, and D miss this structure or info.

🔧 Debug

advanced

Why does swagger-jsdoc return an empty paths object?

You set up swagger-jsdoc with correct options but the generated JSON has an empty 'paths' object. What is the most likely cause?

Express

const options = {
  definition: {
    openapi: '3.0.0',
    info: { title: 'API', version: '1.0' }
  },
  apis: ['./src/routes/*.js']
};
const swaggerSpec = swaggerJSDoc(options);

A The files in './src/routes/*.js' do not contain any JSDoc comments with Swagger annotations

B The 'definition' object is missing the 'servers' property

C The 'apis' path is relative and must be absolute

D The swagger-jsdoc package version is incompatible with OpenAPI 3.0

💡 Hint

swagger-jsdoc extracts API paths from special comments inside the files.

swagger-jsdoc reads the files listed in 'apis' and looks for JSDoc comments with Swagger annotations to build the 'paths' object. If these comments are missing, 'paths' will be empty.

❓ state_output

advanced

What is the effect of calling swaggerJSDoc multiple times with different options?

If you call swaggerJSDoc twice with different 'apis' arrays and merge the results, what will happen?

Express

const spec1 = swaggerJSDoc({ definition: { openapi: '3.0.0', info: { title: 'API1' } }, apis: ['./routes1/*.js'] });
const spec2 = swaggerJSDoc({ definition: { openapi: '3.0.0', info: { title: 'API2' } }, apis: ['./routes2/*.js'] });
const merged = { ...spec1, paths: { ...spec1.paths, ...spec2.paths } };

A swaggerJSDoc caches results and returns the first spec always

B The merged object combines paths from both specs but info will be from spec1 only

C The merged object will throw an error because swaggerJSDoc outputs are not mergeable

D The merged object will only contain paths from spec2

💡 Hint

swaggerJSDoc returns a plain object; merging is manual.

swaggerJSDoc returns a JSON object. Calling it multiple times returns separate specs. Merging paths manually combines endpoints, but other fields like 'info' remain from the first spec unless merged explicitly.

🧠 Conceptual

expert

What is the role of the 'apis' option in swagger-jsdoc?

Why do you specify file paths in the 'apis' option when configuring swagger-jsdoc?

A To tell swagger-jsdoc where to find JSDoc comments with Swagger annotations to generate API documentation

B To specify where swagger-jsdoc should output the generated JSON file

C To list the API endpoints that swagger-jsdoc will automatically create routes for

D To define the order in which API routes are loaded in the Express app

💡 Hint

Think about how swagger-jsdoc knows what to document.

The 'apis' option is an array of file paths or glob patterns. swagger-jsdoc scans these files for JSDoc comments containing Swagger annotations to build the API documentation JSON.

Practice

1. What is the main purpose of swagger-jsdoc in an Express app?

easy

A. To connect to a database

B. To handle HTTP requests and responses

C. To generate API documentation from comments in your code

D. To serve static files like images and CSS

Solution

1. Step 1: Understand swagger-jsdoc role

   swagger-jsdoc reads specially formatted comments in your Express code to create API documentation automatically.

2. Step 2: Compare with other options

   Handling HTTP requests is Express's job, not swagger-jsdoc. Database connection and serving static files are unrelated tasks.

3. Final Answer:

   To generate API documentation from comments in your code -> Option C

4. Quick Check:

   swagger-jsdoc = API docs generator [OK]

Hint: swagger-jsdoc creates docs from code comments [OK]

Common Mistakes:

• Confusing swagger-jsdoc with Express routing
• Thinking swagger-jsdoc manages databases
• Assuming swagger-jsdoc serves static files

2. Which of the following is the correct way to import and initialize swagger-jsdoc in an ES modules-based Express app?

easy

A. import swaggerJSDoc from 'swagger-jsdoc'; const specs = swaggerJSDoc(options);

B. const swaggerJSDoc = require('swagger-jsdoc'); const specs = swaggerJSDoc();

C. const swaggerJSDoc = require('swagger-jsdoc'); const specs = swaggerJSDoc(options);

D. import swaggerJSDoc from 'swagger-jsdoc'; const specs = swaggerJSDoc();

Solution

1. Step 1: Use modern ES module import

   In modern Express apps using ES modules, import swaggerJSDoc from 'swagger-jsdoc' is correct.

2. Step 2: Initialize swagger-jsdoc with options

   swaggerJSDoc requires an options object to generate specs, so calling it without arguments is incorrect.

3. Final Answer:

   import swaggerJSDoc from 'swagger-jsdoc'; const specs = swaggerJSDoc(options); -> Option A

4. Quick Check:

   Import + call with options = C [OK]

Hint: Use import and pass options to swaggerJSDoc() [OK]

Common Mistakes:

• Calling swaggerJSDoc() without options
• Using require instead of import in ES modules
• Not assigning the result to a variable

3. Given this swagger-jsdoc options object, what will specs contain after calling swaggerJSDoc(options)?

const options = {
  definition: {
    openapi: '3.0.0',
    info: { title: 'Test API', version: '1.0.0' }
  },
  apis: ['./routes/*.js']
};
const specs = swaggerJSDoc(options);

medium

A. A string containing raw JavaScript code from './routes/*.js'

B. An object with OpenAPI info and paths extracted from comments in './routes/*.js'

C. An error because 'apis' path is incorrect

D. An empty object because no API comments exist

Solution

1. Step 1: Understand swagger-jsdoc output

   swagger-jsdoc returns a JSON object with OpenAPI info and paths parsed from specified files.

2. Step 2: Check options correctness

   The options specify OpenAPI version and info, and a valid path pattern for API files, so it will parse comments there.

3. Final Answer:

   An object with OpenAPI info and paths extracted from comments in './routes/*.js' -> Option B

4. Quick Check:

   swaggerJSDoc(options) = OpenAPI JSON object [OK]

Hint: swaggerJSDoc returns parsed OpenAPI JSON from code comments [OK]

Common Mistakes:

• Expecting raw code instead of parsed JSON
• Assuming error without checking file existence
• Thinking output is empty without comments

4. Identify the error in this swagger-jsdoc setup snippet:

import swaggerJSDoc from 'swagger-jsdoc';
import swaggerUi from 'swagger-ui-express';
const options = {
  definition: {
    openapi: '3.0.0',
    info: { title: 'API', version: '1.0' }
  },
  apis: ['./api/*.js']
};
const specs = swaggerJSDoc();

app.use('/docs', swaggerUi.serve, swaggerUi.setup(specs));

medium

A. swaggerJSDoc is called without passing the options object

B. The 'apis' path should be './api/*.ts' instead of '.js'

C. swaggerUi.setup() should be called before swaggerUi.serve

D. Missing import for swaggerUi from 'swagger-ui-express'

Solution

1. Step 1: Check swaggerJSDoc call

   The code calls swaggerJSDoc() without arguments, but it requires the options object to generate specs.

2. Step 2: Verify other parts

   The 'apis' path is valid for JavaScript files. swaggerUi.setup() after serve is correct usage.

3. Final Answer:

   swaggerJSDoc is called without passing the options object -> Option A

4. Quick Check:

   Call swaggerJSDoc(options) not empty () [OK]

Hint: Always pass options to swaggerJSDoc() [OK]

Common Mistakes:

• Calling swaggerJSDoc() without options
• Confusing order of swaggerUi middleware
• Ignoring missing imports

5. You want to set up swagger-jsdoc in your Express app to document APIs ONLY in routes/users.js and routes/products.js (assuming there are other .js files in the routes directory that should not be documented). Which apis option correctly includes both files for swagger-jsdoc?

hard

A. ['./routes/users.js', './routes/products']

B. ['./routes/*.js']

C. ['./routes/users.js|./routes/products.js']

D. ['./routes/users.js', './routes/products.js']

Solution

1. Step 1: Understand 'apis' option format

   The 'apis' option is an array of file paths or glob patterns to scan for comments.

2. Step 2: Check each option

   ['./routes/users.js', './routes/products.js'] lists both files explicitly, which is correct. ['./routes/*.js'] uses a glob that includes both files but may include others. ['./routes/users.js|./routes/products.js'] uses an invalid string with '|'. ['./routes/users.js', './routes/products'] has a missing file extension for products.js.

3. Final Answer:

   ['./routes/users.js', './routes/products.js'] -> Option D

4. Quick Check:

   List each file path separately in array [OK]

Hint: List each file path separately in 'apis' array [OK]

Common Mistakes:

• Using invalid string with '|' instead of array items
• Omitting file extensions
• Using too broad glob patterns unintentionally