regexp-to-ast

What is regexp-to-ast?

The `regexp-to-ast` npm package is a utility that converts regular expressions into Abstract Syntax Trees (ASTs). This can be useful for analyzing, transforming, or generating regular expressions programmatically.

What are regexp-to-ast's main functionalities?

Convert RegExp to AST

This feature allows you to convert a regular expression into its corresponding Abstract Syntax Tree (AST). The AST can then be used for further analysis or transformation.

const { regExpParser } = require('regexp-to-ast');
const ast = regExpParser.pattern('/a*b+/');
console.log(JSON.stringify(ast, null, 2));

Analyze AST

This feature demonstrates how to traverse and analyze the AST generated from a regular expression. You can inspect different nodes and their properties.

const { regExpParser } = require('regexp-to-ast');
const ast = regExpParser.pattern('/a*b+/');
function analyzeAST(node) {
  if (node.type === 'Character') {
    console.log(`Character: ${node.value}`);
  }
  if (node.children) {
    node.children.forEach(analyzeAST);
  }
}
analyzeAST(ast);

Other packages similar to regexp-to-ast

regexpp

The `regexpp` package is a regular expression parser for ECMAScript. It provides a way to parse regular expressions into ASTs and offers utilities for AST traversal and manipulation. Compared to `regexp-to-ast`, `regexpp` supports a broader range of ECMAScript regular expression features and provides more detailed AST nodes.

regexp-tree

The `regexp-tree` package is a toolkit for working with regular expressions. It includes a parser that converts regular expressions into ASTs, as well as utilities for transforming and generating regular expressions. `regexp-tree` offers a more comprehensive set of tools for working with regular expressions compared to `regexp-to-ast`.

README

regexp-to-ast

Reads a JavaScript Regular Expression literal(text) and outputs an Abstract Syntax Tree.

Installation

• npm

    npm install regexp-to-ast
  

• Browser

    <script src="https://unpkg.com/regexp-to-ast/lib/parser.js"></script>
  

API

The API is defined as a TypeScript definition file.

Usage

• Parsing to an AST:

  const RegExpParser = require("regexp-to-ast").RegExpParser
  const regexpParser = new RegExpParser.parser()
  
  // from a regexp text
  const astOutput = regexpParser.pattern("/a|b|c/g")
  
  // text from regexp instance.
  const input2 = /a|b/.toString()
  // The same parser instance can be reused
  const anotherAstOutput = regexpParser.pattern(input2)
  

• Visiting the AST:

  // parse to an AST as before.
  const { RegExpParser, BaseRegExpVisitor } = require("regexp-to-ast")
  const regexpParser = new RegExpParser.parser()
  const regExpAst = regexpParser.pattern("/a|b|c/g")
  
  // Override the visitor methods to add your logic.
  class MyRegExpVisitor extends BaseRegExpVisitor {
      visitPattern(node) {}
  
      visitFlags(node) {}
  
      visitDisjunction(node) {}
  
      visitAlternative(node) {}
  
      // Assertion
      visitStartAnchor(node) {}
  
      visitEndAnchor(node) {}
  
      visitWordBoundary(node) {}
  
      visitNonWordBoundary(node) {}
  
      visitLookahead(node) {}
  
      visitNegativeLookahead(node) {}
  
      // atoms
      visitCharacter(node) {}
  
      visitSet(node) {}
  
      visitGroup(node) {}
  
      visitGroupBackReference(node) {}
  
      visitQuantifier(node) {}
  }
  
  const myVisitor = new MyRegExpVisitor()
  myVisitor.visit(regExpAst)
  // extract visit results from the visitor state.
  

Compatibility

This library is written in ES5 style and is compatiable with all major browsers and modern node.js versions.

TODO / Limitations

• Use polyFill for string.prototype.at to support unicode characters outside BMP.
• Descriptive error messages.
• Position information in error messages.
• Support unicode flag escapes.
• Ensure edge cases described in "The madness of parsing real world JavaScript regexps" are supported.
• Support deprecated octal escapes

Changelog

0.5.0 (11-12-2019)

• Added location to AST
  • Thanks to @ConradIrwin :thumbsup