babel-check-duplicated-nodes

1.0.0 verified Sat Apr 25 auth: no javascript

Babel helper utility (v1.0.0) that checks an AST for duplicated nodes, throwing a descriptive error if any are found. Originally extracted from Babel's test fixture runner, this tool helps Babel transform authors catch subtle bugs caused by node reuse. It is a niche package with a single API call, no active release cadence, and is intended for internal use during transform development rather than general production.

Common errors

error TypeError: checkDuplicatedNodes is not a function ↓

cause Default import usage instead of named import.

fix

Use import { checkDuplicatedNodes } from 'babel-check-duplicated-nodes' or const { checkDuplicatedNodes } = require('babel-check-duplicated-nodes').

error Cannot find module 'babel-check-duplicated-nodes' ↓

cause Package not installed or missing from node_modules.

fix

Run npm install babel-check-duplicated-nodes --save-dev.

Warnings

gotcha The pattern 'require('babel-check-duplicated-nodes').default' is incorrect; the package does not have a default export. ↓

fix Use 'const { checkDuplicatedNodes } = require('babel-check-duplicated-nodes')'.

gotcha This package is intended for internal use by Babel transform authors, not for general AST manipulation. Incorrect usage may produce false negatives. ↓

fix Ensure you only call this function on ASTs generated by Babel's parser, not third-party parsers.

Install

npm install babel-check-duplicated-nodes

yarn add babel-check-duplicated-nodes

pnpm add babel-check-duplicated-nodes

Imports

checkDuplicatedNodes

wrong

import checkDuplicatedNodes from 'babel-check-duplicated-nodes'

correct

import { checkDuplicatedNodes } from 'babel-check-duplicated-nodes'

Package exports a named function, not a default export.

Quickstart

Demonstrates how to use checkDuplicatedNodes with @babel/core to detect duplicated AST nodes.

import { checkDuplicatedNodes } from 'babel-check-duplicated-nodes';
import * as babel from '@babel/core';

const code = 'const x = 1; const y = 2;';
const ast = babel.parseSync(code, { filename: 'test.js' });

// Simulate a duplicated node: reuse the same node twice
const duplicateNode = ast.program.body[0];
ast.program.body.push(duplicateNode);

try {
  checkDuplicatedNodes(babel, ast);
} catch (e) {
  console.error(e.message);
}