nearley-loader

2.0.0 verified Sat Apr 25 auth: no javascript

A webpack loader that imports compiled nearley parser grammar files (`.ne` files) directly into JavaScript modules. Current stable version is 2.0.0, compatible with nearley^2.0.0. It integrates with webpack's module bundling, allowing developers to require grammar files and get compiled parser rules. The loader has a peer dependency on nearley, requiring matching major versions. It is commonly used in projects that build parsers with nearley and bundle with webpack. No release cadence is documented; the package is stable but low-maintenance.

Common errors

error Cannot find module 'nearley-loader' ↓

cause nearley-loader is not installed or is a devDependency not resolved.

fix

Run: npm install --save-dev nearley-loader

error Module not found: Error: Can't resolve 'nearley-loader' in ... ↓

cause Webpack cannot locate the loader, likely missing from node_modules.

fix

Ensure nearley-loader is in devDependencies and run npm install.

error TypeError: nearley.Grammar.fromCompiled is not a function ↓

cause Using a very old nearley version (before fromCompiled was introduced, e.g. <2.0.0).

fix

Update nearley to >=2.0.0: npm install nearley@latest

error The 'nearley-loader' loader is not being recognized in webpack.config.js ↓

cause Loader path or regex may be misconfigured; or webpack version is too old.

fix

Use the correct rule definition as shown in the quickstart.

Warnings

gotcha Requiring a grammar file with CommonJS require will import the compiled rules object as default (not a module.exports keyed object). ↓

fix Use ESM import syntax (import grammar from './grammar.ne') for clarity.

gotcha Grammar.fromCompiled must be called on the imported value; passing the raw object to Parser constructor fails. ↓

fix Always use Grammar.fromCompiled(grammar) to get a Grammar instance.

breaking Major version must match nearley's major version. nearley-loader@2.x works only with nearley@^2.0.0; nearley-loader@1.x with nearley@^1.0.0. ↓

fix Install compatible versions: npm install nearley@^2.0.0 nearley-loader@^2.0.0

gotcha create-react-app applies url-loader to unrecognized extensions; .nearley files may be incorrectly handled without override. ↓

fix In CRA, use craco or react-app-rewired to override the webpack config and exclude .nearley from url-loader.

gotcha TypeScript users may need declarations for .ne files; the package does not export types. ↓

fix Add a module declaration: declare module '*.nearley' { const rules: any; export default rules; }

Install

npm install nearley-loader

yarn add nearley-loader

pnpm add nearley-loader

Imports

default import of grammar
wrong
```
const grammar = require('./grammar.ne');
```
correct
```
import grammar from './grammar.ne';
```
ESM import is correct; import returns the compiled rules object.
Parser and Grammar classes
wrong
```
import { Parser, Grammar } from 'nearley-loader';
```
correct
```
import { Parser, Grammar } from 'nearley';
```
Parser and Grammar come from the nearley package, not nearley-loader.
Grammar.fromCompiled
wrong
```
const parser = new Parser(grammar);
```
correct
```
const parser = new Parser(Grammar.fromCompiled(grammar));
```
Grammar.fromCompiled must convert the loader's output; passing it directly to Parser will fail.

Quickstart

Configures webpack to load .nearley files and shows how to use the compiled grammar with nearley's Parser.

// webpack.config.js
module.exports = {
  module: {
    rules: [
      { test: /\.nearley$/i, use: ['nearley-loader'] },
    ],
  },
};

// yourModule.js
import { Parser, Grammar } from 'nearley';
import grammar from './grammar.ne';

const parser = new Parser(Grammar.fromCompiled(grammar));
parser.feed('some input');
console.log(parser.results);