Postman's runtime is based on Node.js. You can use this to write scripts that add dynamic behavior to requests and collections. You can use pre-request and post-response scripts to write API tests, build requests that can contain dynamic parameters, or pass data between requests.
Pre-request and post-response scripts execute asynchronously. That means you can execute multiple scripts without waiting for the previous script to complete. If you want scripts to execute in sequence, you can use a callback function.
You can add JavaScript code to execute during two events in the flow:
Postman will prompt you with suggestions as you enter text. Select one to autocomplete your code.
You can add pre-request and post-response scripts to a collection, a folder, a request within a collection, or a request not saved to a collection.
In Postman, the script execution order for a single request looks like this:
For every request in a collection, scripts will execute in the following order:
For every request in a collection, the scripts will always run according to the same hierarchy. Collection-level scripts will run first, then folder-level scripts, and then request-level scripts. This order of execution applies to both pre-request and post-response scripts.
For example, imagine you had the following collection structured with a single folder and two requests within the folder.
If you created log statements in the pre-request and post-response script sections for the collection, folder, and requests, the execution order is returned in the Postman Console.
The Postman Sandbox is a JavaScript execution environment that's available to you while writing pre-request and post-response scripts for requests (both in Postman and Newman). Whatever code you write in these sections is executed in this sandbox.
You can build conditional workflows using a collection, and branch and loop over a set of requests. To try out this collection template, select Conditional workflow.
You can add commonly used scripts and tests to packages in your team's Package Library. This enables you to reuse scripts in the Pre-request and Post-response tabs in your team's HTTP requests, collections, and folders. Learn how to reuse scripts and tests in Postman.
Debugging scripts can be written under either the Pre-request tab or the Post-response tab. You can log debugging messages in the Postman Console.
You can use post-response script examples to write your own tests for requests, folders, and collections. Post-response scripts execute when Postman receives a response from the API you sent the request to. When you add tests to a folder or collection, they execute after each request inside it.
Postman uses the Faker library to generate sample data, including random names, addresses, email addresses, and more. You can use these predefined variables to return different values per request. Learn how to use dynamic variables.
Postman provides JavaScript APIs that you can use in your request scripts. The pm object provides functionality for testing your request and response data.