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Porffor supports multiple JavaScript and TypeScript parsers, allowing you to choose the best parser for your use case.

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Supported Parsers

Porffor can use any of the following parsers:
  • acorn - Default for JavaScript
  • @babel/parser - Default for TypeScript, full feature support
  • meriyah - Fast, spec-compliant parser
  • hermes-parser - Parser from Hermes JavaScript engine
  • oxc-parser - Oxidation Compiler parser (Rust-based)

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Parser Selection

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--parser
string
default:"acorn | @babel/parser"
Select which parser to use for parsing JavaScript/TypeScript.
# Use meriyah parser
porf --parser=meriyah script.js

# Use Babel parser
porf --parser=@babel/parser script.js

# Use oxc parser
porf --parser=oxc-parser script.js
Default behavior:
  • JavaScript files: acorn
  • TypeScript files: @babel/parser
Source reference: source/compiler/parse.js:9-25

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Parser Details

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Acorn (Default for JS)

porf --parser=acorn script.js
Features:
  • Lightweight and fast
  • Good for standard JavaScript
  • Default for .js files
Parser options: 
{
  ecmaVersion: 'latest',
  sourceType: 'script' | 'module',
  locations: false,
  ranges: false,
  tokens: false,
  comments: false,
  preserveParens: false
}
Source reference: source/compiler/parse.js:31-33

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@babel/parser (Default for TypeScript)

porf --parser=@babel/parser script.ts
Features:
  • Full TypeScript support
  • Supports type annotations
  • Required for --parse-types
  • Default for .ts files
Parser options: 
{
  plugins: ['estree', 'typescript'], // or just ['estree'] for JS
  sourceType: 'script' | 'module',
  locations: false,
  ranges: false,
  tokens: false,
  comments: false,
  preserveParens: false
}
Source reference: source/compiler/parse.js:42

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Meriyah

porf --parser=meriyah script.js
Features:
  • Fast, spec-compliant ECMAScript parser
  • Good performance
  • Supports modern JavaScript features
Parser options: 
{
  next: true,
  module: true,
  webcompat: true,
  raw: true,
  sourceType: 'script' | 'module'
}
Source reference: source/compiler/parse.js:35-39

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Hermes Parser

porf --parser=hermes-parser script.ts
Features:
  • From the Hermes JavaScript engine
  • Supports TypeScript
  • Compatible with React Native

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OXC Parser

porf --parser=oxc-parser script.ts
Features:
  • Rust-based parser (fast)
  • Supports TypeScript
  • Part of the Oxidation Compiler project
Parser options: 
{
  lang: 'js' | 'ts',
  showSemanticErrors: true
}
Source reference: source/compiler/parse.js:52-54

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TypeScript-Compatible Parsers

Only certain parsers support TypeScript syntax: 
porf --parser=@babel/parser script.ts    # ✅ Recommended
porf --parser=hermes-parser script.ts    # ✅ Supported
porf --parser=oxc-parser script.ts       # ✅ Supported
If you use --parse-types with a parser that doesn’t support TypeScript, you’ll receive a warning:
passed -parse-types with a parser (acorn) which does not support
Source reference: source/compiler/parse.js:27

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Force TypeScript Parsing

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-t
flag
Force parsing input as TypeScript, regardless of file extension.
porf -t script.js  # Parse .js file as TypeScript
Automatically uses @babel/parser when enabled.Source reference: source/compiler/parse.js:6

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Module vs Script

Control whether code is parsed as an ES module or a script:
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--module
flag
Parse input as an ES module.
porf --module script.js
Affects the sourceType option passed to all parsers.Differences:
  • Module: Supports import/export, strict mode by default
  • Script: Traditional JavaScript, no imports
Source reference: source/compiler/parse.js:37, 45

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Parser Compatibility Matrix

ParserJavaScriptTypeScriptSpeedNotes
acorn✅❌FastDefault for JS
@babel/parser✅✅MediumDefault for TS, most features
meriyah✅❌FastSpec-compliant
hermes-parser✅✅FastFrom Hermes engine
oxc-parser✅✅Very FastRust-based

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Internal Parser Usage

The parser is loaded dynamically at startup: 
const loadParser = async (fallbackParser = 'acorn', forceParser) => {
  parser = forceParser ?? Prefs.parser ?? fallbackParser;
  const mod = await import(parser);
  parse = mod.parseSync ?? mod.parse;
};
Source reference: source/compiler/parse.js:18-23

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Temporal Detection

All parsers support automatic Temporal API detection: 
if (input.includes('Temporal')) ast._usesTemporal = true;
This loose matching enables Temporal polyfill support when needed. Source reference: source/compiler/parse.js:61

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Examples

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Use fastest parser for production

porf --parser=oxc-parser script.js

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Parse JavaScript with Babel

porf --parser=@babel/parser script.js

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TypeScript with Hermes

porf --parser=hermes-parser app.ts

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Force TypeScript parsing with specific parser

porf -t --parser=oxc-parser script.js

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Error Handling

All parser errors are normalized to SyntaxError: 
try {
  let ast = parse(input, options);
  if (ast.program) ast = ast.program;
  return ast;
} catch (e) {
  throw new SyntaxError(e.message, { cause: e });
}
Source reference: source/compiler/parse.js:64-67

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See Also

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