numeric-literal-parser

A parser for JavaScript numeric literals

$ npm install numeric-literal-parser

const parser = require('numeric-literal-parser');
 
parser.parse('0XdeadBEEF');
/* Output:
   {
     type: 'HexIntegerLiteral',
     prefix: '0X',
     digits: [ 'd', 'e', 'a', 'd', 'B', 'E', 'E', 'F' ]
   } */

Goals

• Correctness: Parse trees should be correct according to the TC39 spec, including Annex B.
• Full Information: Parse trees should have enough information to reproduce the input string. (This parser is intended for static analysis tools, and it's difficult to determine what aspect of the literal a particular tool might care about, so nothing is omitted.)

API

This module exports an object with two properties: parse and SyntaxError. parse is a function that accepts a string and returns a parse tree if the parse was successful, or throws an instance of SyntaxError if the parse was unsuccessful.

Parse trees have the following type:

type ParseTree = 
  {
    type: 'Decimal',
    integralDigits: string[],
    decimalPoint: '.' | null,
    fractionalDigits: string[],
    exponent: {
      exponentIndicator: 'e' | 'E',
      sign: '+' | '-' | null,
      digits: string[]
    } | null
  } |
  {
    type: 'BinaryInteger',
    prefix: '0b' | '0B',
    digits: string[]
  } |
  {
    type: 'OctalInteger',
    prefix: '0o' | '0O',
    digits: string[]
  } |
  {
    type: 'HexInteger',
    prefix: '0x' | '0X',
    digits: string[]
  } |
  {
    type: 'LegacyOctalInteger',
    prefix: '0',
    digits: string[]
  };

Literals are parsed for "sloppy mode" JS. To parse a literal for strict mode JS, run the parser and then throw an error manually if

• the parse tree has type LegacyOctalInteger, or
• the parse tree has type Decimal and multiple integral digits, the first of which is '0'.

Development

The parser specification in grammar.pegjs. Run npm run build to generate the JavaScript module.

License

MIT License