Extracting data from responses in Postman

Introduction

We extract data from responses to use it in later tests or requests. This helps us check if the system works correctly step-by-step.

When you want to save a user ID from a login response to use in another request.

When you need to get a token from a response to authorize future requests.

When you want to check if a specific value appears in the response data.

When you want to pass data dynamically between multiple API calls in a test collection.

Syntax

Postman

pm.test("Extract value from response", function () {
    var jsonData = pm.response.json();
    pm.environment.set("keyName", jsonData.data.id);
});

Use pm.response.json() to parse the response body as JSON.

Use pm.environment.set("key", value) to save data for later use.

Examples

This saves the token from the response into an environment variable called userToken.

Postman

pm.test("Save user token", function () {
    var jsonData = pm.response.json();
    pm.environment.set("userToken", jsonData.token);
});

This saves the order.id into a collection variable named orderId.

Postman

pm.test("Extract order ID", function () {
    var jsonData = pm.response.json();
    pm.collectionVariables.set("orderId", jsonData.order.id);
});

This checks if the response status code is 200 (OK).

Postman

pm.test("Check response status", function () {
    pm.response.to.have.status(200);
});

Sample Program

This test extracts the user.id from the JSON response and saves it as an environment variable userID. It also checks that the ID is a number.

Postman

pm.test("Extract user ID from response", function () {
    var jsonData = pm.response.json();
    pm.environment.set("userID", jsonData.user.id);
    pm.expect(jsonData.user.id).to.be.a('number');
});

Important Notes

Always check the response format before extracting data to avoid errors.

Use environment or collection variables to share data between requests.

Use descriptive variable names to keep your tests clear.

Summary

Extracting data helps connect multiple API requests in tests.

Use pm.response.json() to read JSON responses.

Save data with pm.environment.set() or pm.collectionVariables.set().

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