Extracting data from responses in Postman - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Extracting a single value from JSON response

Given the following Postman test script, what will be the value of userId after execution if the response body is {"user":{"id":42,"name":"Alice"}}?

Postman

const responseJson = pm.response.json();
const userId = responseJson.user.id;

A "42"

B undefined

C null

D 42

💡 Hint

Remember that JSON numbers are parsed as numbers, not strings.

The response JSON has a user object with an id property of number 42. Accessing responseJson.user.id returns the number 42.

❓ assertion

intermediate

Correct assertion to check extracted value

Which Postman test assertion correctly verifies that the extracted token from the JSON response {"auth":{"token":"abc123"}} is exactly "abc123"?

Postman

const responseJson = pm.response.json();
const token = responseJson.auth.token;

A pm.test('Token is abc123', () => { pm.expect(token).to.be.a('number'); });

B pm.test('Token is abc123', () => { pm.expect(token).to.be.true; });

C pm.test('Token is abc123', () => { pm.expect(token).to.eql('abc123'); });

D pm.test('Token is abc123', () => { pm.expect(token).to.have.length(5); });

💡 Hint

Check the exact value and type of the token string.

Option C correctly asserts that token equals the string 'abc123'. Other options check unrelated conditions.

🔧 Debug

advanced

Debugging extraction from nested JSON array

You want to extract the id of the first item in the items array from this response: {"data":{"items":[{"id":10},{"id":20}]}}. The code below returns undefined. What is the problem?

Postman

const responseJson = pm.response.json();
const firstItemId = responseJson.items[0].id;

A The code should access responseJson.data.items[0].id instead of responseJson.items[0].id.

B The responseJson is not parsed correctly; use pm.response.text() instead.

C The items array is empty, so accessing index 0 returns undefined.

D The id property does not exist on the items objects.

💡 Hint

Check the full path to the items array in the JSON structure.

The items array is inside the data property, so the correct path is responseJson.data.items[0].id.

🧠 Conceptual

advanced

Understanding Postman environment variable extraction

Which statement correctly describes how to extract a value from a JSON response and save it as an environment variable in Postman?

A Use pm.environment.set('varName', value) after extracting the value from pm.response.json().

B Use pm.variables.get('varName') to save the extracted value.

C Use pm.response.save('varName', value) to store the value.

D Use pm.request.set('varName', value) to save the extracted value.

💡 Hint

Remember the method to set environment variables in Postman scripts.

pm.environment.set('varName', value) saves a variable in the environment scope for later use.

❓ framework

expert

Choosing the correct Postman test script for conditional extraction

You want to extract the sessionId from the response only if the status code is 200. Which Postman test script correctly implements this conditional extraction?

A if (pm.response.statusCode === 200) { const sessionId = pm.response.json().sessionId; pm.environment.set('sessionId', sessionId); }

B if (pm.response.code === 200) { const sessionId = pm.response.json().sessionId; pm.environment.set('sessionId', sessionId); }

C if (pm.response.code == '200') { const sessionId = pm.response.json().sessionId; pm.environment.set('sessionId', sessionId); }

D if (pm.response.status === 200) { const sessionId = pm.response.json().sessionId; pm.environment.set('sessionId', sessionId); }

💡 Hint

Check the exact property name for status code in Postman response object.

pm.response.code is the correct property for the numeric status code. pm.response.status is a string like 'OK'.

Practice

1. What is the primary purpose of extracting data from API responses in Postman?

easy

A. To reuse data in subsequent API requests

B. To change the API endpoint URL

C. To modify the request headers

D. To delete the response data

Solution

1. Step 1: Understand the role of data extraction

   Extracting data allows you to capture values from one response to use later.

2. Step 2: Connect API requests using extracted data

   This helps chain requests by passing data like tokens or IDs forward.

3. Final Answer:

   To reuse data in subsequent API requests -> Option A

4. Quick Check:

   Extract data = reuse in next requests [OK]

Hint: Extract data to pass info between requests [OK]

Common Mistakes:

• Thinking extraction changes the URL
• Confusing extraction with header modification
• Believing extraction deletes data

2. Which Postman script correctly extracts the value of userId from a JSON response and saves it as an environment variable?

easy

A. let data = pm.response.json(); pm.environment.set('userId', data.userId);

B. pm.response.set('userId', pm.response.json().userId);

C. pm.environment.get('userId', pm.response.json().userId);

D. let userId = pm.response.set('userId');

Solution

1. Step 1: Use pm.response.json() to parse JSON

   This method converts the response body into a JavaScript object.

2. Step 2: Use pm.environment.set() to save variable

   Set the environment variable 'userId' with the extracted value.

3. Final Answer:

   let data = pm.response.json(); pm.environment.set('userId', data.userId); -> Option A

4. Quick Check:

   Parse JSON + set env variable = let data = pm.response.json(); pm.environment.set('userId', data.userId); [OK]

Hint: Use pm.response.json() then pm.environment.set() [OK]

Common Mistakes:

• Using pm.response.set() which doesn't exist
• Using pm.environment.get() to set variables
• Not parsing JSON before accessing properties

3. Given the response body:

{"token": "abc123", "user": {"id": 42}}

What will this Postman script save in the environment variable authToken?

let jsonData = pm.response.json();
pm.environment.set('authToken', jsonData.token);

medium

A. null

B. 42

C. undefined

D. "abc123"

Solution

1. Step 1: Parse the JSON response

   jsonData.token accesses the 'token' key which has value "abc123".

2. Step 2: Set environment variable with token value

   pm.environment.set saves "abc123" as 'authToken'.

3. Final Answer:

   "abc123" -> Option D

4. Quick Check:

   jsonData.token = "abc123" [OK]

Hint: Access exact key from parsed JSON to get value [OK]

Common Mistakes:

• Using user.id instead of token
• Expecting number 42 instead of string token
• Not parsing JSON before accessing token

4. You wrote this Postman test script to extract sessionId from the response:

let data = pm.response.json();
pm.environment.set('sessionId', data.session_id);

But the environment variable sessionId is always empty. What is the likely problem?

medium

A. pm.response.json() does not parse JSON

B. pm.environment.set() cannot save variables

C. The response JSON uses sessionId not session_id

D. You must use pm.collectionVariables.set() instead

Solution

1. Step 1: Check JSON key names carefully

   The script uses 'session_id' but the response likely has 'sessionId' (camelCase).

2. Step 2: Correct key name to match response

   Use data.sessionId to correctly extract the value.

3. Final Answer:

   The response JSON uses sessionId not session_id -> Option C

4. Quick Check:

   Key name mismatch causes empty variable [OK]

Hint: Match JSON keys exactly, including case [OK]

Common Mistakes:

• Assuming pm.environment.set() doesn't work
• Not parsing JSON before accessing keys
• Confusing environment and collection variables

5. You receive this nested JSON response:

{"data": {"users": [{"id": 1, "name": "Alice"}, {"id": 2, "name": "Bob"}]}}

How do you extract and save the name of the second user as a collection variable in Postman?

hard

A. pm.environment.set('secondUserName', pm.response.json().data.users[1].name);

B. let json = pm.response.json(); pm.collectionVariables.set('secondUserName', json.data.users[1].name);

C. let json = pm.response.json(); pm.environment.set('secondUserName', json.data.users[2].name);

D. pm.collectionVariables.set('secondUserName', pm.response.json().users[2].name);

Solution

1. Step 1: Parse the nested JSON response

   Access the array at json.data.users and select index 1 for the second user.

2. Step 2: Save the second user's name as a collection variable

   Use pm.collectionVariables.set with key 'secondUserName' and value json.data.users[1].name.

3. Final Answer:

   let json = pm.response.json(); pm.collectionVariables.set('secondUserName', json.data.users[1].name); -> Option B

4. Quick Check:

   Index 1 in users array = second user name [OK]

Hint: Use zero-based index and correct variable scope [OK]

Common Mistakes:

• Using index 2 instead of 1 for second user
• Mixing environment and collection variables
• Not parsing JSON before accessing nested data