Skip to content
Postman API Testing Tips

What Language Can You Use With Postman

API Testing Blog

What Languages Can You Use With Postman?

Postman’s primary function is to act as a powerful tool for interacting with APIs, allowing you to send requests, receive responses, and perform testing. While the user interface provides a visual way to construct requests, Postman also offers flexibility by letting you incorporate scripting languages to automate complex tasks. This guide will explore the languages you can use within Postman to enhance your API testing workflow.

Postman’s Native Scripting Language: JavaScript

Postman’s built-in scripting language is JavaScript, providing extensive capabilities for manipulating requests, responses, data, and more. It empowers you to write custom logic within the platform.

Example: Verifying a JSON Response

This code snippet checks if a response contains a specific JSON property:

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


pm.test("Response has 'message' field", function () {
  pm.expect(pm.response.json().message).to.be.a('string');
});

Explanation:

  1. pm.test("Test Description", function () {}): Defines a test case with a clear description.
  2. pm.response.to.have.status(200): Verifies the status code of the response.
  3. pm.expect(pm.response.json().message).to.be.a('string'): Asserts the existence and data type of a specific field within the JSON response.

How to Use JavaScript in Postman:

  1. Test Tab: Within the Postman interface, click on the “Test” tab of your request.
  2. Code Editor: You’ll find a code editor where you can write your JavaScript code.
  3. Run Tests: To execute your tests, click the “Send” button and navigate to the “Tests” tab to view the results.

Pre-Request Scripts: Setting Up Requests Dynamically

Pre-request scripts are JavaScript functions that execute before a request is sent. They allow you to manipulate request parameters, headers, or even the request URL itself.

Example: Dynamically Adding an Authorization Token

// Get the token from environment variable
let token = pm.environment.get("AUTH_TOKEN");


// Add the token to the Authorization header
pm.request.headers.Authorization = `Bearer ${token}`;

Explanation:

  1. pm.environment.get("AUTH_TOKEN"): Retrieves the token value stored in an environment variable named “AUTH_TOKEN”.
  2. pm.request.headers.Authorization: Sets the Authorization header value to the token, using “Bearer” authentication.

How to Use Pre-Request Scripts:

  1. Pre-request Tab: Within the Postman interface, go to the “Pre-request” tab of your request.
  2. Code Editor: Use the code editor to write your pre-request script.

Environment Variables and Collections

Postman enables you to create environment variables, acting like placeholders for dynamic values. These variables can be used in requests, scripts, and pre-request scripts. They can be managed within collections – organized sets of requests along with their associated environments and scripts.

Example: Using Environment Variables for URLs

// Set the environment variable 'BASE_URL' in your Postman environment
pm.environment.set("BASE_URL", "https://api.example.com");


// Access the variable in your request URL
pm.request.url.path = `${pm.environment.get("BASE_URL")}/users`;

Explanation:

  1. pm.environment.set("BASE_URL", "https://api.example.com"): Sets the value of the environment variable “BASE_URL” to the API endpoint.
  2. pm.environment.get("BASE_URL"): Retrieves the value of the “BASE_URL” environment variable in the request.

How to Use Environment Variables and Collections:

  1. Environment Tab: In Postman, access the “Environments” tab to define and manage environment variables.
  2. Collections Tab: Navigate to the “Collections” tab to create collections, group requests, and associate environments with them.

Beyond JavaScript: Runners and External Libraries

While JavaScript is the foundation of Postman scripting, you can further enhance your testing capabilities by integrating with external tools and libraries:

  • Postman Runners: Run tests in different environments and configure them to send notifications based on test results.
  • External Libraries: Leverage external libraries such as ChaiJS (assertion library), SinonJS (mocking framework), and Lodash (utility library) to increase functionality.

Powerful Testing with Languages in Postman

By leveraging JavaScript and the integration possibilities within Postman, you gain tremendous control over your API testing process. From dynamic requests to detailed assertions, your testing strategy can be seamlessly incorporated into your workflow, enhancing efficiency and accuracy.

API Testing Blog