jisu

JISU

A work in progress JavaScript tokeniser and parser. Currently only supports a subset of the JavaScript language and is not ECMAScript compliant.

Install via npm install jisu

An online demo is available at https://ben-sb.github.io/jisu

About

JISU is a recursive descent parser (roughly). I say roughly as it uses the precedence climbing method to parse binary and logical expressions.

Currently I've been working on this in my free time, which I don't have a lot of right now, but I do plan to continue supporting more of the JS language, and may eventually start using this parser in production at my company (Ocule) if it reaches that level. I may also write some AST manipulation tools for the obfuscation/deobfuscation enjoyers out there.

Specs

The repo has two exports:

• parse - Parses a full program
• parseExpression - Parses a single expression

Both take the input as a string and optionally a set of parser options.

interface ParserOptions {
    emitLogs?: boolean;
    omitLocations?: boolean;
}

I'm a big fan of Babel and as a result the format of the AST JISU produces is extremely similar to Babel's. As a result @babel/generator can be used on the AST (as seen in src/demo.ts). I also took inspiration from the @babel/types package and implemented a similar system in src/parser/ast.

Tests

Unit tests can be run via npm test
Currently there are very few tests but I plan to add more.

To Do

• Rewrite object member parsing
• Allow semi-keywords (e.g. await, async, of) to be treated as identifiers
• Support numbers expressed in hexadecimal, octal and scientific notation
• Support regular expressions
• Probably a lot more

To Fix

• Object patterns are treated as normal object expressions even when not used as a pattern
• Spread elements are allowed in sequence expressions
• Spread elements are allowed on their own in parenthesised expressions