npm i ts-pegjs


Plugin for pegjs to generate TypeScript parsers.

by metadevpro

3.1.0 (see all)License:MITTypeScript:Not Found
npm i ts-pegjs


TS PEG.js is a TS code generation plugin for peggy.

Build Status Known Vulnerabilities npm version





Installs ts-pegjs + peggy

$ npm install ts-pegjs


Generating a Parser from JS code

In Node.js, require both the peggy parser generator and the ts-pegjs plugin:

var peggy = require('peggy');
var tspegjs = require('ts-pegjs');

To generate a TS parser, pass to pegjs.generate ts-pegjs plugin and your grammar:

var parser = pegjs.generate("start = ('a' / 'b')+", {
    output: 'source',
    format: 'commonjs',
    plugins: [tspegjs],
    tspegjs: {
        customHeader: "// import lib\nimport { Lib } from 'mylib';"

The method will return source code of generated parser as a string.

Supported options of pegjs.generate:

  • cache — if true, makes the parser cache results, avoiding exponential parsing time in pathological cases but making the parser slower (default: false). This is strongly recommended for big grammars (like javascript.pegjs or css.pegjs in example folder)
  • allowedStartRules — rules the parser will be allowed to start parsing from (default: the first rule in the grammar)

Plugin options

Note: Options in CLI mode are written in POSIX (long names as kebab-case) convention e.g. --custom-header but with camelcase on JavaScript e.g. customHeader.

  • customHeader — A string or an array of strings which are a valid TS code to be injected on the header of the output file. E.g. provides a convenient place for adding library imports.
  • customHeaderFile — A header file to include.
  • errorName — The name of the exported internal error class to override. The default value from version 3.0.0 is PeggySyntaxError. Previous one was SyntaxError.
  • returnTypes — An object containing rule names as keys and a valid TS return type as string.

Generating a Parser from CLI

Sample usage:

peggy --plugin ./src/tspegjs -o examples/arithmetics.ts --cache examples/arithmetics.pegjs

(Note ./src/tspegjs is the path to tspegjs.js in the project. If you installed ts-pegjs using npm, it should probably be ./node_modules/ts-pegjs/src/tspegjs.)

It will generarate the parser in the TS flavour.

If you need to pass specific plugin options you can use the option --extra-options-file provided by pegjs and pass it a filename (e.g. pegconfig.json) containing specific options like the following JSON sample:

peggy --plugin ./src/tspegjs --extra-options-file pegconfig.json -o examples/arithmetics.ts --cache examples/arithmetics.pegjs
    "tspegjs": {
        "customHeader": "// import lib\nimport { Lib } from 'mylib';"
    "returnTypes": {
        "Integer": "number",
        "Expression": "number",

For rules not listed in returnTypes object any type is declared by default.

Make sure to pass any additional CLI options, like --extra-options-file before the parameter -o as these will otherwise be treated as arguments to that one.

Using the Parser

  1. Save parser generated by pegjs.generate to a file or use the one generated from the CLI tool.

  2. In client TS code:

import { PeggySyntaxError, parse } from './arithmetics';

try {
    const sampleOutput = parse('my sample...');
} catch (ex: PeggySyntaxError) {
    // Handle parsing error
    // [...]




Thanks to:


The MIT License (MIT)

(c) 2017-2023, Pedro J. Molina at metadev.pro

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