Pre-request Scripts

Run a small JavaScript snippet before a request is sent. Pre-request scripts are useful for setting environment variables dynamically - for example, generating a timestamp, computing a signature, or reading a value that changes between requests.

Where to Write Scripts

Open a saved request and click the Pre-request tab in the request form. A dot appears on the tab label when a script is present.

The editor provides autocompletion for all available globals.

Available Globals

environment

Read and write variables in the active environment.

Method	Description
environment.get(key)	Returns the current value of key, or an empty string if the variable does not exist
environment.set(key, value)	Sets the current value of key in the active environment

environment.set() writes to the variable's current value, which is a local override stored separately from the committed environments.json file. This means scripts never cause unintended git changes. See Environments: Initial Value and Current Value for details.

request

Read-only view of the outgoing request.

Property	Type	Description
request.method	string	HTTP method, e.g. "GET"
request.url	string	Full URL before variable substitution
request.headers	Record<string, string> | undefined	Request headers
request.body	string | undefined	Raw request body

Example

// Set a timestamp for use in a signed request
environment.set('timestamp', new Date().toISOString());

// Compute a derived value from an existing variable
const baseToken = environment.get('apiToken');
environment.set('authHeader', 'Bearer ' + baseToken);

After the script runs, any variables set with environment.set() are applied before variable substitution happens. This means you can set {{timestamp}} in a header and the pre-request script will supply its value.

Execution Order

1. Pre-request script runs
2. Environment variables are updated with any overrides from the script
3. Variable substitution replaces {{placeholders}} in the URL, headers, and body
4. The request is sent

Limitations

• Scripts time out after 5 seconds
• No network access (fetch and XMLHttpRequest are not available)
• No require or import - scripts run in an isolated sandbox
• No async/await - scripts must be synchronous
• Only enabled variables in the active environment are visible to environment.get()