nodebnf

1.0.1 verified Fri May 01 auth: no javascript

BNF is a JavaScript library for compiling, parsing, and interpreting BNF and ABNF grammars. Version 1.0.1 uses ECMAScript 6+ and supports inline compilation of grammars, predefined rules (e.g., DIGIT, CRLF, LITERAL), rule events, and multi-language scripts (planned). It runs on Node.js. Unlike other parser generators (e.g., PEG.js, ANTLR), BNF focuses on simplicity and direct embedding of BNF/ABNF syntax without a separate generation step. The library is in early development, with custom rule APIs subject to change.

Common errors

error TypeError: compiler.AddLanguage is not a function ↓

cause Importing the library incorrectly (e.g., default import or wrong path).

fix

Use import { Compiler } from 'bnf'; and instantiate with new Compiler().

error Error: No language registered ↓

cause Calling ParseScript before AddLanguage.

fix

Ensure AddLanguage is called with a valid grammar before parsing.

error SyntaxError: Unexpected token ↓

cause Invalid BNF/ABNF syntax (e.g., missing angle brackets or incorrect repeat notation).

fix

Validate grammar using BNF syntax: <rule> ::= <expression> | "literal" or ABNF: rule = expression / "literal".

Warnings

breaking Custom BNF rules API is unstable and will change during minor version updates. ↓

fix Avoid writing custom rules until v2 stabilizes, or pin to a specific minor version.

deprecated The prior version used a custom JavaScript markup for script files; this feature is removed in v1. ↓

fix Migrate to inline compiling with AddLanguage and ParseScript.

gotcha Method names are PascalCase (e.g., AddLanguage, ParseScript) unlike typical JavaScript camelCase. ↓

fix Use exactly the documented casing: AddLanguage, SetRuleEvents, ParseScript.

gotcha The predefined rule SYNTAX must be declared in every grammar; missing it causes parse failure. ↓

fix Always include a rule named SYNTAX as the entry point.

Install

npm install bnf

yarn add bnf

pnpm add bnf

Imports

Compiler
wrong
```
const Compiler = require('bnf').Compiler
```
correct
```
import { Compiler } from 'bnf'
```
ESM import path is 'bnf'. The package may also support CommonJS require, but ESM is preferred for v1.
BNF
wrong
```
const bnf = require('bnf')
```
correct
```
import { BNF } from 'bnf'
```
BNF is a named export. Do not default-import.

ABNF

wrong

import ABNF from 'bnf'

correct

import { ABNF } from 'bnf'

ABNF is a named export, not default.

Quickstart

Creates a compiler, adds a calculator grammar, sets rule events, and parses expressions.

import { Compiler } from 'bnf';

const compiler = new Compiler();
compiler.AddLanguage(`
  <SYNTAX> ::= <evaluation> | <evaluation> <CRLF> <SYNTAX>
  <evaluation> ::= <number> <OWSP> <type> <OWSP> <number>
  <number> ::= <DIGITS>
  <type> ::= "+" | "-" | "/" | "*"
`, "testLang");
compiler.SetRuleEvents({
  evaluation(token) {
    console.log("evaluation token found answer:", eval(token.value));
  }
});
compiler.ParseScript(`
5456 / 13
11 + 3
10 * 8
`.trim());