TS PEG.js

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

Requirements

• PEG.js

Installation

Node.js

Install PEG.js with ts-pegjs plugin

$ npm install ts-pegjs

Usage

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": {
        "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

• 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": {
        "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
    // [...]
}

Changelog

Changelog.

Acknowledgments

Thanks to:

• David Majda for creating pegjs
• Futago-za Ryuu for maintain pegjs
• Elantcev Mikhail for providing the pegjs PHP plugin, inspiration on this one.

License

The MIT License (MIT)

(c) 2017-2021, Pedro J. Molina at metadev.pro