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0.2.7 • Public • Published


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

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Install PEG.js with ts-pegjs plugin

$ npm install ts-pegjs


Generating a Parser from JS code

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

var pegjs = require("pegjs");
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": {
        "noTslint": false,
        "tslintIgnores": "rule1,rule2",
        "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

  • no-tslint — Excludes the default tslint rules exclusions (defaults to false).
  • tslint-ignores — A custom list of tslint rules to be excluded (comma separated, if no provided, a default tslint rule exclusion list will be applied).
  • custom-header — A custom header of TS code to be injected on the header of the output file. E.g. provides a convenient place for adding library imports.
  • returnTypes — An object containing rule names as keys and return type as string.

Generating a Parser from CLI

Sample usage:

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

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:

pegjs --plugin ./src/tspegjs --extra-options-file pegconfig.json -o examples/arithmetics.ts --cache examples/arithmetics.pegjs
    "tspegjs": {
        "noTslint": false,
        "tslintIgnores": "rule1,rule2",
        "customHeader": "// import lib\nimport { Lib } from 'mylib';"

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


Thanks to:


The MIT License (MIT)

(c) 2017-2018, Pedro J. Molina at metadev.pro


npm i ts-pegjs

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