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Scripts

Automate your workflow with pre-request and post-request scripts using JavaScript.

Overview

Scripts let you run JavaScript code before a request is sent (pre-request) or after a response is received (post-request). Use them to set variables, modify requests dynamically, validate responses, or chain requests together.

Echolon provides a scripting API giving you access to environment variables, request data, and response data through global objects.

Note: Scripts run in a sandboxed environment with access to common JavaScript utilities like JSON, Date, Math, btoa, atob, and more.

Pre-request Scripts

Pre-request scripts run before your request is sent. They're perfect for:

  • Generating timestamps or random values
  • Computing authentication signatures
  • Setting dynamic headers or body content
  • Reading and setting environment variables

Example: Adding a timestamp header

// Add a timestamp to every request
req.setHeader('X-Request-Time', Date.now().toString());
console.log('Request will be sent at:', new Date().toISOString());

Post-request Scripts

Post-request scripts run after the response is received. Use them to:

  • Validate status codes and response bodies
  • Extract values (like tokens) to use in subsequent requests
  • Log response data for debugging
  • Store values in environment variables

Example: Extracting and storing a token

// Parse response and store auth token
const data = JSON.parse(res.body);
if (data.token) {
  echo.setEnvVar('auth_token', data.token);
  console.log('Token saved to environment');
}
console.log('Response status:', res.status);

Scripting API

Echolon provides three global objects in scripts: echo, req, and res.

echo Object

The echo object provides methods to interact with environment and runtime variables.

Method Description
echo.getEnvVar(name) Get an environment variable value
echo.setEnvVar(name, value) Set an environment variable (persists for the session)
echo.getVar(name) Get a runtime variable (request-scoped)
echo.setVar(name, value) Set a runtime variable (request-scoped)
echo.sleep(ms) Pause execution for specified milliseconds

Example:

// Get base URL from environment
const baseUrl = echo.getEnvVar('baseUrl');
console.log('Using base URL:', baseUrl);

// Set a variable for later use
echo.setEnvVar('lastRequestTime', Date.now().toString());

req Object

The req object provides access to the current request. In pre-request scripts, you can both read and modify the request.

Property/Method Description
req.url The request URL (read/write)
req.method The HTTP method (read/write)
req.headers Headers object (read/write)
req.body Request body (read/write)
req.getUrl() Get the request URL
req.setUrl(url) Set the request URL
req.getMethod() Get the HTTP method
req.setMethod(method) Set the HTTP method
req.getHeaders() Get all headers as an object
req.getHeader(name) Get a specific header value (case-insensitive)
req.setHeaders(headers) Replace all headers
req.setHeader(name, value) Set a specific header
req.getBody() Get the request body
req.setBody(body) Set the request body

Example:

// Log current request details
console.log('Making', req.method, 'request to', req.url);

// Add authentication header
const token = echo.getEnvVar('auth_token');
if (token) {
  req.setHeader('Authorization', 'Bearer ' + token);
}

// Modify the request body
const body = JSON.parse(req.getBody() || '{}');
body.timestamp = Date.now();
req.setBody(JSON.stringify(body));

res Object

The res object is available only in post-request scripts and provides read-only access to the response.

Property/Method Description
res.status HTTP status code (e.g., 200, 404)
res.statusText HTTP status text (e.g., "OK", "Not Found")
res.headers Response headers object
res.body Response body as string
res.responseTime Request duration in milliseconds
res.getStatus() Get the status code
res.getStatusText() Get the status text
res.getHeaders() Get all headers as an object
res.getHeader(name) Get a specific header (case-insensitive)
res.getBody() Get the response body
res.getResponseTime() Get the response time in ms

Example:

// Check response status
if (res.status !== 200) {
  console.error('Request failed with status:', res.status, res.statusText);
}

// Parse JSON response
try {
  const data = JSON.parse(res.body);
  console.log('Response data:', data);
  
  // Store user ID for next request
  if (data.id) {
    echo.setEnvVar('userId', data.id.toString());
  }
} catch (e) {
  console.error('Failed to parse response as JSON');
}

// Log performance
console.log('Request completed in', res.responseTime, 'ms');

Sample Scripts

Echolon includes built-in sample scripts to help you get started. Access them from the dropdown menu in the Scripts tab.

Pre-request Script Examples

Set Environment Variable

// Set an environment variable
echo.setEnvVar('my_env_variable', 'my_env_value');
console.log('Environment variable set: my_env_variable');

Add Authentication Header

// Add Bearer token authentication
const token = echo.getEnvVar('auth_token');
if (token) {
  req.setHeader('Authorization', 'Bearer ' + token);
  console.log('Added auth header');
} else {
  console.warn('No auth token found in environment');
}

Generate Timestamp

// Add timestamp to request
const timestamp = Date.now();
req.setHeader('X-Timestamp', timestamp.toString());
console.log('Timestamp:', new Date(timestamp).toISOString());

Generate UUID

// Generate a simple UUID v4
const uuid = 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, (c) => {
  const r = Math.random() * 16 | 0;
  const v = c === 'x' ? r : (r & 0x3 | 0x8);
  return v.toString(16);
});
echo.setVar('requestId', uuid);
req.setHeader('X-Request-ID', uuid);
console.log('Generated UUID:', uuid);

Post-request Script Examples

Log Response

// Log response details
console.log('Status:', res.status, res.statusText);
console.log('Response time:', res.responseTime, 'ms');
console.log('Body preview:', res.body.substring(0, 200));

Extract Token

// Extract and store auth token from response
try {
  const data = JSON.parse(res.body);
  if (data.token || data.access_token) {
    const token = data.token || data.access_token;
    echo.setEnvVar('auth_token', token);
    console.log('Token extracted and saved');
  }
} catch (e) {
  console.error('Could not parse response:', e.message);
}

Validate Response

// Validate response status and content
if (res.status >= 400) {
  console.error('Request failed:', res.status, res.statusText);
} else {
  console.log('Request successful');
  
  // Check content type
  const contentType = res.getHeader('content-type');
  if (contentType && contentType.includes('application/json')) {
    const data = JSON.parse(res.body);
    console.log('Response contains', Object.keys(data).length, 'fields');
  }
}

Viewing Script Output

After sending a request, script output (console logs, errors) appears in the Scripts tab in the response panel. This tab shows:

  • Pre-request output: Logs from the pre-request script
  • Post-request output: Logs from the post-request script
  • Execution time: How long each script took to run
  • Errors: Any script errors with stack traces
Scripts output
Debugging tip: Use console.log(), console.warn(), console.error(), and console.info() to output debug information. All console output is captured and displayed in the Scripts tab.

Available Globals

In addition to echo, req, and res, scripts have access to:

  • console — log, warn, error, info methods
  • JSON — parse and stringify
  • Date — date manipulation
  • Math — mathematical operations
  • btoa / atob — Base64 encoding/decoding
  • encodeURIComponent / decodeURIComponent
  • parseInt, parseFloat, isNaN, isFinite
  • Array, Object, String, Number, Boolean