js library

JavaScript execution support for web_query

This library provides JavaScript execution capabilities for extracting variables from obfuscated or eval-based JavaScript code.

The JavaScript runtime clears global variables only when a query uses jseval transforms, and only once per QueryString.execute() call. This prevents variable pollution between queries while maximizing efficiency. The runtime is never disposed (which causes crashes), only cleared.

Variable Detection

Auto-detect (jseval without variable names) captures:

• Variables declared with var in global scope (e.g., var COOKIE_DOMAIN = 'example.com')
• Variables added to window or globalThis
• Common patterns like __INITIAL_STATE__, __NEXT_DATA__, etc.

It CANNOT detect:

• Variables declared with let or const (block-scoped, inaccessible)
• Variables in function scope

Example:

var userId = 123;           // ✓ Auto-detected
window.config = {...};      // ✓ Auto-detected
let userName = "Alice";     // ✗ NOT detected (block-scoped)
const API_KEY = "secret";   // ✗ NOT detected (block-scoped)

For let/const variables, you must use other extraction methods like transform=json:variableName which uses regex pattern matching.

Usage:

import 'package:web_query/js.dart';

// Basic configuration
configureJsExecutor(FlutterJsExecutor());

// Extract specific variables (recommended)
final result = QueryString('script/@text?transform=jseval:config,userData')
    .getValue(node);

// Wildcard matching
final flashvars = QueryString('script/@text?transform=jseval:flashvars_*')
    .getValue(node);

// Multiple patterns
final data = QueryString('script/@text?transform=jseval:*_config,*_data')
    .getValue(node);

// Auto-detect (limited to global variables)
final all = QueryString('script/@text?transform=jseval')
    .getValue(node);

// Configure with custom limits
configureJsExecutor(FlutterJsExecutor(
  maxScriptSize: 2 * 1024 * 1024,  // 2MB script limit
  maxResultSize: 20 * 1024 * 1024, // 20MB result limit
  truncateLargeScripts: true,       // Truncate instead of reject
));