Variable assignment in flows in Postman

Introduction

Variable assignment in flows helps you store and reuse data during your API tests. It makes your tests flexible and easier to manage.

When you want to save a value from the API response to use later in the same request.

When you need to keep track of data like tokens or IDs within the current request execution.

When you want to change a variable value based on test results dynamically.

When you want to avoid hardcoding values and make tests reusable.

When you want to pass data between different parts of the same request (pre-request script, tests, etc.).

Syntax

Postman

pm.variables.set('variable_name', value);
pm.variables.get('variable_name');

Use pm.variables.set to assign a value to a variable.

Use pm.variables.get to retrieve the value later in the flow.

Examples

This sets a variable userId to 12345 and then gets it to use later.

Postman

pm.variables.set('userId', 12345);
const id = pm.variables.get('userId');

This saves a token from the API response JSON to a variable for later use.

Postman

pm.variables.set('token', pm.response.json().token);
const token = pm.variables.get('token');

Sample Program

This script saves the user ID from the API response, retrieves it, prints it, and checks that it is a number.

Postman

// Save user ID from response
pm.variables.set('userId', pm.response.json().id);

// Use saved user ID in this request
const userId = pm.variables.get('userId');
console.log(`User ID is: ${userId}`);

// Check if userId is set correctly
pm.test('User ID is assigned', function () {
    pm.expect(userId).to.be.a('number');
});

Important Notes

Variables set with pm.variables.set last only during the current request execution.

To keep variables across requests, consider using pm.environment.set or pm.collectionVariables.set.

Always check if the value you want to assign exists in the response to avoid errors.

Summary

Variable assignment lets you save and reuse data during API tests.

Use pm.variables.set to assign and pm.variables.get to retrieve values.

This makes your tests flexible and easier to maintain.

Practice

1. What does pm.variables.set('token', 'abc123') do in a Postman test script?

easy

A. It saves the value 'abc123' to a variable named 'token' for later use.

B. It retrieves the value of the variable 'token'.

C. It deletes the variable named 'token'.

D. It sends 'abc123' as a request header named 'token'.

Solution

1. Step 1: Understand the method pm.variables.set

   This method assigns a value to a variable in Postman scripts.

2. Step 2: Analyze the parameters

   The first parameter is the variable name 'token', the second is the value 'abc123' to store.

3. Final Answer:

   It saves the value 'abc123' to a variable named 'token' for later use. -> Option A

4. Quick Check:

   pm.variables.set saves data [OK]

Hint: Set stores data; get retrieves it [OK]

Common Mistakes:

• Confusing set with get method
• Thinking set deletes variables
• Assuming set sends data in requests

2. Which of the following is the correct syntax to assign a variable named 'userId' with value 42 in a Postman test script?

easy

A. pm.variables.get('userId', 42);

B. pm.variables.store('userId', 42);

C. pm.variables.assign('userId' = 42);

D. pm.variables.set('userId', 42);

Solution

1. Step 1: Recall the correct method for assigning variables

   The method to assign a variable is pm.variables.set(name, value).

2. Step 2: Check each option's syntax

   pm.variables.set('userId', 42); uses pm.variables.set('userId', 42); which is correct syntax.

3. Final Answer:

   pm.variables.set('userId', 42); -> Option D

4. Quick Check:

   Use pm.variables.set to assign [OK]

Hint: Set method assigns variables with (name, value) [OK]

Common Mistakes:

• Using get instead of set to assign
• Incorrect method names like assign or store
• Wrong parameter syntax with equals sign

3. Consider this Postman test script snippet:

pm.variables.set('count', 5);
pm.variables.set('count', pm.variables.get('count') + 3);
console.log(pm.variables.get('count'));

What will be printed in the console?

medium

A. 5

B. 8

C. Error

D. undefined

Solution

1. Step 1: Analyze the first assignment

   The variable 'count' is set to 5 initially.

2. Step 2: Analyze the second assignment

   It gets the current 'count' value (5), adds 3, and sets 'count' to 8.

3. Step 3: Check the console.log output

   It prints the updated value of 'count', which is 8.

4. Final Answer:

   8 -> Option B

5. Quick Check:

   5 + 3 = 8 [OK]

Hint: Get current value, add, then set updated value [OK]

Common Mistakes:

• Assuming the first value stays unchanged
• Thinking get returns undefined
• Confusing set and get usage

4. You wrote this Postman test script:

pm.variables.set('status', 'active')
pm.variables.get('status')

But the test fails because the variable 'status' is undefined. What is the likely cause?

medium

A. Variables set in one request are not available in another without environment or global scope.

B. pm.variables.get returns undefined if set is not awaited.

C. Missing semicolon after set statement causes failure.

D. Variable names cannot be strings.

Solution

1. Step 1: Understand variable scopes in Postman

   Variables set with pm.variables.set are local to the current request script and do not persist across requests.

2. Step 2: Identify why 'status' is undefined

   If you try to get 'status' in a different request without using environment or global variables, it will be undefined.

3. Final Answer:

   Variables set in one request are not available in another without environment or global scope. -> Option A

4. Quick Check:

   Local variables don't persist across requests [OK]

Hint: Use environment/global variables for cross-request data [OK]

Common Mistakes:

• Thinking semicolons affect variable persistence
• Believing get waits for set automatically
• Assuming variable names can't be strings

5. You want to save a user token from a response JSON and reuse it in the next request. Which flow correctly assigns and retrieves the token using Postman variables?

hard

A. In first request test script: pm.variables.set('token', pm.response.json().token);In next request pre-request script: const token = pm.environment.get('token');

B. In first request test script: pm.variables.set('token', pm.response.json().token);In next request pre-request script: const token = pm.variables.get('token');

C. In first request test script: pm.environment.set('token', pm.response.json().token);In next request pre-request script: const token = pm.environment.get('token');

D. In first request test script: pm.environment.set('token', pm.response.json().token);In next request pre-request script: const token = pm.variables.get('token');

Solution

1. Step 1: Identify variable scope for cross-request use

   To reuse data across requests, environment variables must be used, not local variables.

2. Step 2: Match correct set and get methods

   In first request test script: pm.environment.set('token', pm.response.json().token);
   In next request pre-request script: const token = pm.environment.get('token'); uses pm.environment.set and pm.environment.get, which correctly share data between requests.

3. Final Answer:

   Use environment variables to save and retrieve token across requests. -> Option C

4. Quick Check:

   Environment variables persist across requests [OK]

Hint: Use environment variables for data between requests [OK]

Common Mistakes:

• Using pm.variables for cross-request data
• Mixing environment and local variable methods
• Not retrieving variables in the correct scope