Cherow NPM | npm.io

Cherow

In active development!!

A very fast and lightweight, standards-compliant, self-hosted javascript parser with high focus on both performance and stability.

Features

Conforms to the standard ECMAScript® 2018 (ECMA-262 9th Edition) language specification
Supports Stage 3 proposals via option
Optionally track syntactic node locations
Emits an ESTree-compatible abstract syntax tree.
Very well tested (~23 000 unit tests with full code coverage))
Lightweight - 62 KB minified

ESNext features

Stage 3 features support. These need to be enabled with the next option.

Builds

Cherow contains 3 different builds:

Name	Description
`Stable`	Stable release
`Next`	Has the `next` option enabled by default, and support all latest ECMAScript proposals.
`Bleeding`	The active development branch. You can and will expect bugs with this branch because it's not stable

API

Cherow 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 and this is achieved by choosing parseScript function to parse a script and parseModule function to parse a module.

Here is a quick example:

cherow.parseScript('const fooBar = 123;', { ranges: true });

This will return when serialized in json:

{
    "type": "Program",
    "sourceType": "script",
    "body": [
        {
            "type": "VariableDeclaration",
            "declarations": [
                {
                    "type": "VariableDeclarator",
                    "init": {
                        "type": "Literal",
                        "value": 123,
                        "start": 15,
                        "end": 18
                    },
                    "id": {
                        "type": "Identifier",
                        "name": "fooBar",
                        "start": 6,
                        "end": 12
                    },
                    "start": 6,
                    "end": 18
                }
            ],
            "kind": "const",
            "start": 0,
            "end": 19
        }
    ],
    "start": 0,
    "end": 19
}

Options

There is a second argument to both methods that allows you to specify various options:

Option	Description
`delegate`	Accepts a callback function to be invoked for each syntax node (as the node is constructed)
`loc`	Attach line/column location information to each node
`ranges`	Append start and end offsets to each node
`globalReturn`	Allow return in the global scope
`skipShebang`	Allow to skip shebang - '#'
`impliedStrict`	Enable implied strict mode
`next`	Enable stage 3 support (ESNext)
`source`	Set to true to record the source file in every node's `loc` object when the `loc option` is set.
`raw`	Attach raw property to each literal node

Modules

In Cherow this replace the traditional plugin system, and let you import the parser instance and develop your own functions with it, and / or re-use existing one.

Example:

import { parser, scanSignedInteger, parseScript, parserModule } from 'cherow';

function doWhatYouWant(parser, context) {
    // do some magic with numbers
    value = scanSignedInteger(parser, context); / '+', '-'

    // ...
}

Performance

Benchmark #1

Alt text

Benchmark #2

Note! This Jazzle parser couldn't parse the TypeScript library, so the results is not 100%.

Alt text

parsing ecmascript typescript parser performance tolerant estree es2018 es2019 ECMAScript 2019 esnext javascript ast jsx tolerant lightweight

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