acorn-loose

import { parse, isDummy } from 'acorn-loose'; import { parse as strictParse } from 'acorn'; // Recommended peer dependency for strict parsing import { generate } from 'astring'; // A common AST utility for code generation const invalidCode = ` function example(arg1, arg2,) { // Trailing comma in params is okay in ES2017+ if (true { // Missing parenthesis and closing brace return "hello"; `; let ast; try { // Always attempt strict parsing first for valid code strictParse(invalidCode, { ecmaVersion: 2020, sourceType: 'module' }); } catch (e: any) { console.log('Strict parser failed as expected:', e.message.split('\n')[0]); // Fallback to acorn-loose for error-tolerant parsing of malformed code ast = parse(invalidCode, { ecmaVersion: 2020, sourceType: 'module' }); console.log('AST generated by acorn-loose (first few nodes):', JSON.stringify(ast.body.slice(0, 2), null, 2)); let dummyCount = 0; // Simple traversal to find dummy nodes (a dedicated AST walker like acorn.walk is recommended for full traversal) function traverse(node: any) { if (node && typeof node === 'object') { if (isDummy(node)) { dummyCount++; } for (const key in node) { // Avoid circular references and properties that may not contain nodes (e.g., 'parent') if (Object.prototype.hasOwnProperty.call(node, key) && key !== 'parent' && typeof node[key] === 'object') { traverse(node[key]); } } } } traverse(ast); console.log(`Found ${dummyCount} dummy nodes in the AST.`); console.log('Attempting to regenerate code (may be malformed due to error recovery):\n', generate(ast)); }