Scripting Overview

Scripting lets you run small pieces of JavaScript around a request — to prepare data before it is sent and to process the response after it arrives.

What scripting is for

Common uses include:

• Setting or computing variables before a request runs.
• Calculating signatures, timestamps, or other dynamic values.
• Extracting values from a response to chain into the next request.
• Asserting on responses with tests.

The Jint sandbox

Scripts run in a sandboxed JavaScript engine (Jint). The sandbox is deliberately restrictive so that running a collection cannot harm your machine:

• No filesystem access — scripts cannot read or write files.
• No process access — scripts cannot spawn processes or read the environment.
• Hard limits on memory, execution time, and recursion depth — a runaway script is stopped automatically.

Caution

Because of these limits, scripting is for lightweight request logic — not for heavy computation or accessing external resources.

Pre-request vs post-response

There are two kinds of script:

Type	Runs	Typical use
Pre-request	Before the request is sent	Set variables, mutate headers, compute values
Post-response	After the response is received	Read the response, extract values, branch logic

Where scripts live

Scripts can be attached at three levels, each with its own tab:

• Request — runs for that single request.
• Folder — runs for every request in the folder.
• Collection — runs for every request in the collection.

This lets you put shared setup (for example refreshing a token) on the collection and keep request-specific logic local.

The scripting objects at a glance

Scripts interact with the run through three objects:

Object	Available in	Purpose
bru	Both	Read and write variables and the environment
req	Both	Inspect and mutate the outgoing request
res	Post-response only	Read the response

A test() / expect() API is also available for writing assertions.

See the Scripting API reference for the full list of members.