Timestamp generation in Postman - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Postman test script timestamp?

Consider this Postman test script snippet that generates a timestamp in milliseconds since Unix epoch. What will be the value of timestamp after running this code?

Postman

const timestamp = Date.now();
console.log(timestamp);

A Undefined, because Date.now() is not a function in Postman scripts

B A string with the current date in ISO format, e.g., '2023-06-17T12:00:00.000Z'

C An object containing date and time properties

D A number representing milliseconds since January 1, 1970, e.g., 1687000000000

💡 Hint

Date.now() returns the current time in milliseconds as a number.

Date.now() returns the number of milliseconds elapsed since January 1, 1970 (Unix epoch). It is a number, not a string or object.

❓ assertion

intermediate

Which assertion correctly verifies a timestamp is recent in Postman?

You want to write a test in Postman to check that a timestamp variable responseTimestamp is within the last 5 seconds. Which assertion is correct?

Postman

const responseTimestamp = pm.response.json().timestamp;
const now = Date.now();

A pm.expect(responseTimestamp).to.be.within(now - 5000, now);

B pm.expect(responseTimestamp).to.equal(now - 5000);

C pm.expect(responseTimestamp).to.be.above(now + 5000);

D pm.expect(responseTimestamp).to.be.a('string');

💡 Hint

Check if the timestamp is between now minus 5 seconds and now.

The assertion to.be.within(now - 5000, now) checks if responseTimestamp is between 5 seconds ago and now, which means it is recent.

🔧 Debug

advanced

Why does this Postman script fail to generate a valid timestamp?

This Postman test script tries to generate a timestamp but fails. What is the error?

Postman

const timestamp = new Date().getTime;
console.log(timestamp);

A timestamp is a function reference, not a number, because getTime is missing parentheses

B timestamp is a string instead of a number

C timestamp is undefined because Date() is not called correctly

D SyntaxError due to missing semicolon

💡 Hint

Check if getTime is called as a function.

getTime is a function and must be called with parentheses (). Without them, timestamp holds the function itself, not the time value.

🧠 Conceptual

advanced

What is the difference between Date.now() and new Date().getTime() in Postman scripts?

Both Date.now() and new Date().getTime() return timestamps. What is the key difference?

A <code>Date.now()</code> returns seconds; <code>new Date().getTime()</code> returns milliseconds

B <code>Date.now()</code> returns a string; <code>new Date().getTime()</code> returns a number

C <code>Date.now()</code> is a static method returning milliseconds; <code>new Date().getTime()</code> creates a Date object then returns milliseconds

D There is no difference; both return the current date as a formatted string

💡 Hint

One creates an object, the other does not.

Date.now() is a static method that returns the current timestamp in milliseconds directly. new Date().getTime() creates a Date object first, then returns the timestamp.

❓ framework

expert

How to reliably test timestamp freshness in Postman for asynchronous APIs?

You have an API that returns a timestamp of when data was last updated. The timestamp is in milliseconds. You want to write a Postman test that passes only if the timestamp is within 10 seconds of the current time, accounting for network delay. Which approach is best?

Postman

const responseTimestamp = pm.response.json().lastUpdated;
const now = Date.now();

A Use <code>pm.expect(responseTimestamp).to.be.a('string');</code> to verify type

B Use <code>pm.expect(responseTimestamp).to.be.within(now - 10000, now + 1000);</code> to allow 1 second future tolerance

C Use <code>pm.expect(responseTimestamp).to.equal(now);</code> for exact match

D Use <code>pm.expect(responseTimestamp).to.be.below(now - 10000);</code> to check if timestamp is older than 10 seconds

💡 Hint

Allow some tolerance for network delays and clock differences.

Because of network delays and slight clock differences, allowing a small future tolerance (e.g., 1 second) ensures the test does not fail incorrectly. Checking within 10 seconds plus a small future window is best practice.

Practice

1. What does Date.now() return in Postman scripts?

easy

A. The current date as a string in format YYYY-MM-DD

B. The current time zone offset in minutes

C. The current timestamp in milliseconds since January 1, 1970

D. The current time in seconds since midnight

Solution

1. Step 1: Understand Date.now() function

   Date.now() returns the number of milliseconds elapsed since January 1, 1970 00:00:00 UTC.

2. Step 2: Compare options with this definition

   Only The current timestamp in milliseconds since January 1, 1970 correctly describes this behavior as a timestamp in milliseconds.

3. Final Answer:

   The current timestamp in milliseconds since January 1, 1970 -> Option C

4. Quick Check:

   Date.now() = milliseconds timestamp [OK]

Hint: Remember: Date.now() gives milliseconds since 1970 [OK]

Common Mistakes:

• Thinking Date.now() returns a formatted date string
• Confusing milliseconds with seconds
• Assuming it returns time zone info

2. Which of the following is the correct way to save the current timestamp in a Postman environment variable?

easy

A. pm.environment.set('currentTime', Date.now());

B. pm.environment.get('currentTime', Date.now());

C. pm.environment.save('currentTime', Date.now());

D. pm.environment.store('currentTime', Date.now());

Solution

1. Step 1: Identify the correct method to set environment variables

   In Postman scripts, pm.environment.set(key, value) is used to save a variable.

2. Step 2: Check each option's method name

   Only pm.environment.set('currentTime', Date.now()); uses the correct method set with the right syntax.

3. Final Answer:

   pm.environment.set('currentTime', Date.now()); -> Option A

4. Quick Check:

   Use pm.environment.set() to save variables [OK]

Hint: Use pm.environment.set() to save variables [OK]

Common Mistakes:

• Using pm.environment.get() to save variables
• Using non-existent methods like save() or store()
• Forgetting to pass both key and value

3. What will be the output of this Postman test script snippet?

let start = Date.now();
pm.environment.set('startTime', start);
let end = Date.now();
pm.environment.set('endTime', end);
let duration = pm.environment.get('endTime') - pm.environment.get('startTime');
console.log(duration);

medium

A. A negative number due to subtraction order

B. Zero, because start and end are set at the same time

C. Undefined, because variables are not saved correctly

D. A positive number representing milliseconds elapsed between start and end

Solution

1. Step 1: Understand the timestamp capture

   start and end capture timestamps at two different moments, so end ≥ start.

2. Step 2: Calculate duration

   Subtracting start from end gives the elapsed time in milliseconds, which is positive or zero.

3. Final Answer:

   A positive number representing milliseconds elapsed between start and end -> Option D

4. Quick Check:

   duration = end - start ≥ 0 [OK]

Hint: Subtract start from end timestamps for elapsed time [OK]

Common Mistakes:

• Assuming start and end are identical
• Confusing subtraction order causing negative result
• Thinking variables are not saved properly

4. You wrote this Postman script to save a timestamp:

pm.environment.set('timeStamp', Date.now)

Why does this cause an error or unexpected behavior?

medium

A. Date.now is a function and needs parentheses to execute

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

C. The variable name 'timeStamp' is reserved

D. Date.now returns a string, not a number

Solution

1. Step 1: Check usage of Date.now

   Date.now is a function reference, not the timestamp itself.

2. Step 2: Identify missing parentheses

   To get the current timestamp, you must call the function with (), like Date.now().

3. Final Answer:

   Date.now is a function and needs parentheses to execute -> Option A

4. Quick Check:

   Call Date.now() with () to get timestamp [OK]

Hint: Always add () to call Date.now() function [OK]

Common Mistakes:

• Forgetting parentheses after Date.now
• Thinking pm.environment.set can't save numbers
• Assuming variable names cause errors

5. You want to measure the response time of an API request in Postman using timestamps. Which script correctly captures the start time before the request and calculates the duration after the response?

hard

A. In Tests: pm.environment.set('startTime', Date.now());In Pre-request Script: let duration = Date.now() - pm.environment.get('startTime');

B. In Pre-request Script: pm.environment.set('startTime', Date.now());In Tests: let duration = Date.now() - pm.environment.get('startTime');
pm.test('Response time', () => pm.expect(duration).to.be.below(2000));

C. In Pre-request Script: let duration = Date.now() - pm.environment.get('startTime');In Tests: pm.environment.set('startTime', Date.now());

D. In Tests: let duration = pm.environment.get('startTime') - Date.now();In Pre-request Script: pm.environment.set('startTime', Date.now());

Solution

1. Step 1: Capture start time before request

   The Pre-request Script runs before the API call, so saving startTime there is correct.

2. Step 2: Calculate duration after response

   The Tests script runs after the response, so subtracting startTime from current time gives elapsed time.

3. Final Answer:

   captures the start time before the request and calculates the duration after the response -> Option B

4. Quick Check:

   Pre-request sets start; Tests calculate duration [OK]

Hint: Set start time pre-request; calculate duration in tests [OK]

Common Mistakes:

• Setting start time after request instead of before
• Subtracting timestamps in wrong order
• Calculating duration before request runs