JavaScript Scripting API Overview

January 18, 2026 · View on GitHub

LazyCurl provides a powerful JavaScript scripting API for automating request workflows, testing responses, and managing data dynamically.

Runtime: Goja JavaScript engine (ES5.1+)

For the complete single-page reference, see Scripting API Reference.

Script Types
Quick Reference
The lc Global Object
Getting Started
API Modules

Script Types

Type	Execution	Use Case
Pre-request	Before HTTP request is sent	Add auth headers, modify URL, generate dynamic data
Post-response	After HTTP response received	Validate response, extract data, run tests

Quick Reference

Core Modules

Module	Description	Docs
`lc.request`	HTTP request manipulation (URL, headers, body, params)	14 methods/properties
`lc.response`	HTTP response access (status, headers, body)	7 methods/properties
`lc.env`	Environment variables (persisted to file)	5 methods
`lc.globals`	Session variables (in-memory)	6 methods
`lc.test`	Test definitions and assertions	16 matchers

Utility Modules

Module	Description	Docs
`lc.cookies`	Cookie management	7 methods
`lc.crypto`	Hash functions and HMAC	7 methods
`lc.base64`	Base64 encoding/decoding	4 methods
`lc.variables`	Dynamic data generation	12 methods
`lc.info`	Execution context info	6 properties
`lc.sendRequest`	Request chaining	1 method
`console`	Logging	5 methods

The `lc` Global Object

All scripting APIs are accessible through the lc global object:

// Pre-request: Add authentication header
var token = lc.env.get("auth_token");
if (token) {
    lc.request.headers.set("Authorization", "Bearer " + token);
}

// Post-response: Validate and store data
lc.test("Status is 200", function() {
    lc.expect(lc.response.status).toBe(200);
});

var data = lc.response.body.json();
if (data && data.token) {
    lc.env.set("auth_token", data.token);
}

Getting Started

1. Add a Pre-request Script

Navigate to the Pre-request tab in the Request panel and add:

// Add timestamp header
lc.request.headers.set("X-Request-Time", Date.now().toString());

// Add API key from environment
var apiKey = lc.env.get("api_key");
if (apiKey) {
    lc.request.headers.set("X-API-Key", apiKey);
}

2. Add a Post-response Script

Navigate to the Post-response tab and add:

// Log response info
console.log("Status: " + lc.response.status);
console.log("Time: " + lc.response.time + "ms");

// Run tests
lc.test("Response is successful", function() {
    lc.expect(lc.response.status).toBe(200);
});

lc.test("Response has data", function() {
    var data = lc.response.body.json();
    lc.expect(data).not.toBeNull();
});

3. Send the Request

Press Ctrl+S to send. View results in:

Console tab: Script logs
Tests tab: Assertion results

API Modules

Request & Response

lc.request - Read and modify the HTTP request
- lc.request.method - HTTP method (read-only)
- lc.request.url - Request URL
- lc.request.headers.* - Header manipulation
- lc.request.body.* - Body access/modification
- lc.request.params.* - Query parameter access
lc.response - Access HTTP response data
- lc.response.status - HTTP status code
- lc.response.headers.* - Response headers
- lc.response.body.* - Response body

Variables

lc.env - Environment variables persisted to disk
lc.globals - Session variables in memory

Testing

lc.test - Define tests with lc.test(name, fn)
lc.expect - Fluent assertions

Utilities

lc.cookies - Cookie management
lc.crypto - Cryptographic hash functions
lc.base64 - Base64 encoding/decoding
lc.variables - Generate random test data
lc.info - Script execution context
lc.sendRequest - Chain multiple requests
console - Logging functions