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# Test and debug values in gRPC requests using JavaScript in Postman

Postman has a powerful scripting environment that enables you to add JavaScript code (scripts) in your gRPC requests, collections, and folders. You can define scripts for three hooks available during the request run lifecycle:

* Before invoking the method and establishing a connection with the server, in the **Before invoke** tab.
* When the client receives a message from the server, in the **On message** tab.
* After closing the connection with the server, in the **After response** tab.

You can use scripts to write API tests, debug your requests by logging to [Postman Console](/docs/use/send-requests/response-data/troubleshooting-api-requests/), or dynamically read/update the values of [variables](/docs/use/send-requests/variables/variables/). You can [import packages](/docs/tests-and-scripts/write-scripts/packages/package-library/) with scripts and tests from your team's Postman Package Library. You can also [import packages from external package registries](/docs/tests-and-scripts/write-scripts/packages/external-package-registries/), such as npm and JSR.

> **Info**
>
> Once you invoke your gRPC request, updates to scripts in the **On message** tab won't take effect until the next time you invoke the request.

![gRPC scripts](https://assets.postman.com/postman-docs/v11/sending-requests-grpc-scripting-in-grpc-request-v11.66.0.jpg)

The [Postman Sandbox](/docs/tests-and-scripts/write-scripts/postman-sandbox-reference/overview/) is available to you when you write your **Before invoke**, **On message**, and **After response** scripts. The sandbox is a JavaScript runtime environment where your scripts run.

To learn more about Postman test scripts, see [Write scripts to test API response data in Postman](/docs/tests-and-scripts/write-scripts/test-scripts/).