Meriyah

100% compliant, self-hosted javascript parser with high focus on both performance and stability. Stable and already used in production.

Demo

Features

• Conforms to the standard ECMAScript® 2020 (ECMA-262 10th Edition) language specification
• Support TC39 proposals via option
• Support for additional ECMAScript features for Web Browsers
• JSX support via option
• Optionally track syntactic node locations
• Emits an ESTree-compatible abstract syntax tree.
• No backtracking
• Low memory usage
• Very well tested (~99 000 unit tests with full code coverage)
• Lightweight - ~90 KB minified

ESNext features

• Decorators
• Class Public Instance Fields & Private Instance Fields
• Hashbang grammar
• import.meta
• Nullish coalescing Operator
• Numeric separators
• Optional Chaining
• Private methods
• Static class fields and private static methods

Note: These features need to be enabled with the next option.

Installation

npm install meriyah --save-dev

API

Meriyah generates AST according to ESTree AST format, and can be used to perform syntactic analysis (parsing) of a JavaScript program, and with ES2015 and later a JavaScript program can be either a script or a module.

The parse method exposed by meriyah takes an optional options object which allows you to specify whether to parse in script mode (the default) or in module mode.

This is the available options:

{
  // The flag to allow module code
  module: false;

  // The flag to enable stage 3 support (ESNext)
  next: false;

  // The flag to enable start and end offsets to each node
  ranges: false;

  // Enable web compability
  webcompat: false;

  // The flag to enable line/column location information to each node
  loc: false;

  // The flag to attach raw property to each literal and identifier node
  raw: false;

  // Enabled directives
  directives: false;

  // The flag to allow return in the global scope
  globalReturn: false;

  // The flag to enable implied strict mode
  impliedStrict: false;

  // Allows comment extraction. Accepts either a function or array
  onComment: []

  // Allows token extraction. Accepts either a function or array
  onToken: []

  // Enable non-standard parenthesized expression node
  preserveParens: false;

  // Enable lexical binding and scope tracking
  lexical: false;

  // Adds a source attribute in every node’s loc object when the locations option is `true`
  source: false;

  // Distinguish Identifier from IdentifierPattern
  identifierPattern: false;

   // Enable React JSX parsing
  jsx: false

  // Allow edge cases that deviate from the spec
  specDeviation: false
}

Example usage:

import { parseScript } from './meriyah';

parseScript('({x: [y] = 0} = 1)');

This will return when serialized in json:

{
    type: "Program",
    sourceType: "script",
    body: [
        {
            type: "ExpressionStatement",
            expression: {
                type: "AssignmentExpression",
                left: {
                    type: "ObjectPattern",
                    properties: [
                        {
                            type: "Property",
                            key: {
                                type: "Identifier",
                                name: "x"
                            },
                            value: {
                                type: "AssignmentPattern",
                                left: {
                                    type: "ArrayPattern",
                                    elements: [
                                        {
                                            "type": "Identifier",
                                            "name": "y"
                                        }
                                    ]
                                },
                                right: {
                                    type: "Literal",
                                    value: 0
                                }
                            },
                            kind: "init",
                            computed: false,
                            method: false,
                            shorthand: false
                        }
                    ]
                },
                operator: "=",
                right: {
                    type: "Literal",
                    value: 1
                }
            }
        }
    ]
}