Scripting in Postman

Postman's runtime is based on Node.js and lets you 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, pass data between requests, and more.

Pre-request and post-response scripts execute asynchronously. This enables you to execute multiple scripts without waiting for the previous script to complete. If you'd like scripts to execute in sequence, you can use a callback function.

Scripts in Postman

You can add JavaScript code to execute during two events in the flow:

1. Before a request is sent to the server, as a pre-request script under the Scripts > Pre-request tab.
2. After a response is received, as a post-response script under the Scripts > Post-response tab.

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.

Execution order of scripts

In Postman, the script execution order for a single request looks like this:

• A pre-request script associated with a request will execute before the request is sent
• A post-response script associated with a request will execute after the request is sent

For every request in a collection, scripts will execute in the following order:

• A pre-request script associated with a collection will run prior to every request in the collection.
• A pre-request script associated with a folder will run prior to every direct child request in the folder.
• A post-response script associated with a collection will run after every request in the collection.
• A post-response script associated with a folder will run after every direct child request in the folder.

For every request in a collection, the scripts will always run according to the same hierarchy. Collection-level scripts (if any) will run first, then folder-level scripts (if any), and then request-level scripts (if any). Note that 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.

How it works

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.

Reuse scripts

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

Debugging scripts can be written under either the Pre-request tab or the Post-response tab, with helpful messages logged in the Postman Console.