meriyah
Meriyah
100% compliant, self-hosted javascript parser with high focus on both performance and stability. Stable and already used in production.
Interactive Playground Benchmark
Features
- Conforms to the standard ECMAScript® 2024 (ECMA-262 15th Edition) language specification
- Except RegExp duplicate named groups (See RegExp support)
- Support some TC39 stage 3 proposals via option "next"
- Support for additional ECMAScript features for Web Browsers (Annex B)
- JSX support via option "jsx"
- Does NOT support TypeScript or Flow syntax
- Track syntactic node locations with option "ranges" or "loc"
- Emits an ESTree-compatible abstract syntax tree
- No backtracking
- Low memory usage
ESNext Stage 3 features
Supported stage 3 features:
These features need to be enabled with the next option.
Not yet supported stage 3 features:
RegExp support
Meriyah doesn't parse RegExp internal syntax, ESTree spec didn't require internal structure of RegExp. Meriyah does use JavaScript runtime to validate the RegExp literal. That means Meriyah's RegExp support is only as good as JavaScript runtime's RegExp support.
As of Auguest 2024, some latest RegExp features are not supported due to missing implementation in general JavaScript runtime.
- RegExp modifiers (stage 3) is not supported
- RegExp duplicate named groups is not supported
In addition, RegExp v flag (unicodeSets) only works on Nodejs v20+ and latest browsers.
Installation
npm install meriyah --save-devAPI
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.
// There are also "parseScript" and "parseModule" exported.
import { parse } from 'meriyah';
const result = parse('let some = "code";', { ranges: true });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, end offsets and range: [start, end] to each node
ranges: false;
// Enable web compatibility
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;
// 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 detection of automatic semicolon insertion. Accepts a callback function that will be passed the charater offset where the semicolon was inserted
onInsertedSemicolon: (pos) => {};
// 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: undefined; // Set to source: 'source-file.js'
// Enable React JSX parsing
jsx: false;
}onComment and onToken
If an array is supplied, comments/tokens will be pushed to the array, the item in the array contains start/end/range information when ranges flag is true, it will also contain loc information when loc flag is true.
If a function callback is supplied, the signature must be
declare function onComment(type: string, value: string, start: number, end: number, loc: SourceLocation): void;
declare function onToken(token: string, start: number, end: number, loc: SourceLocation): void;Note the start/end/loc information are provided to the function callback regardless of the settings on ranges and loc flags. onComment callback has one extra argument value: string for the body string of the comment.
onInsertedSemicolon
If a function callback is supplied, the signature must be
declare function onInsertedSemicolon(position: number): void;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
}
}
}
]
}