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.
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 (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.
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, with helpful messages logged in the Postman Console.
Last modified: 2021/01/27
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