character-parser

What is character-parser?

The character-parser npm package is designed for parsing through strings to identify and handle different characters or sequences of characters. It is particularly useful in scenarios where you need to process code or text to find specific patterns, such as brackets, quotes, or custom-defined sequences. This package can be utilized in developing compilers, interpreters, or any application that requires detailed analysis of text or code.

What are character-parser's main functionalities?

Bracket Matching

This feature allows you to parse through a string to find matching brackets. It's useful for syntax analysis in code editors or compilers.

const characterParser = require('character-parser');
let content = 'function(a, b) { return a + b; }';
let state = characterParser.defaultState();
for (let i = 0; i < content.length; i++) {
  state = characterParser.parseChar(content.charAt(i), state);
  if (state.isNesting()) {
    console.log('Nesting at index', i);
  }
}

String Detection

This feature helps in identifying when the parser is within a string. It's particularly useful for syntax highlighting or escaping strings in code.

const characterParser = require('character-parser');
let content = '"Hello, world!" and 'another string'';
let state = characterParser.defaultState();
for (let i = 0; i < content.length; i++) {
  state = characterParser.parseChar(content.charAt(i), state);
  if (state.isString()) {
    console.log('Inside a string at index', i);
  }
}

Other packages similar to character-parser

acorn

Acorn is a robust, full-featured JavaScript parser that can parse ECMAScript code. It provides detailed analysis of script structure, which makes it more comprehensive than character-parser for JavaScript-specific projects but potentially heavier for simple character parsing tasks.

esprima

Esprima is another JavaScript parser that supports ECMAScript 5.1 and newer versions. It's used for static analysis and code manipulation. Compared to character-parser, Esprima offers more detailed parsing capabilities specific to JavaScript syntax but might be overkill for basic character parsing needs.

chevrotain

Chevrotain is a fast and feature-rich parser building toolkit for JavaScript. Unlike character-parser, which is focused on character-level parsing, Chevrotain provides tools for creating complex parsers and interpreters, making it suitable for building full programming languages or complex domain-specific languages (DSLs).

README

character-parser

Parse JavaScript one character at a time to look for snippets in Templates. This is not a validator, it's just designed to allow you to have sections of JavaScript delimited by brackets robustly.

Installation

npm install character-parser

Usage

Work out how much depth changes:

var state = parse('foo(arg1, arg2, {\n  foo: [a, b\n');
assert(state.roundDepth === 1);
assert(state.curlyDepth === 1);
assert(state.squareDepth === 1);
parse('    c, d]\n  })', state);
assert(state.squareDepth === 0);
assert(state.curlyDepth === 0);
assert(state.roundDepth === 0);

Bracketed Expressions

Find all the contents of a bracketed expression:

var section = parser.parseMax('foo="(", bar="}") bing bong');
assert(section.start === 0);
assert(section.end === 16);//exclusive end of string
assert(section.src = 'foo="(", bar="}"');


var section = parser.parseMax('{foo="(", bar="}"} bing bong', {start: 1});
assert(section.start === 1);
assert(section.end === 17);//exclusive end of string
assert(section.src = 'foo="(", bar="}"');

The bracketed expression parsing simply parses up to but excluding the first unmatched closed bracket (), }, ]). It is clever enough to ignore brackets in comments or strings.

Custom Delimited Expressions

Find code up to a custom delimiter:

var section = parser.parseUntil('foo.bar("%>").baz%> bing bong', '%>');
assert(section.start === 0);
assert(section.end === 17);//exclusive end of string
assert(section.src = 'foo.bar("%>").baz');

var section = parser.parseUntil('<%foo.bar("%>").baz%> bing bong', '%>', {start: 2});
assert(section.start === 2);
assert(section.end === 19);//exclusive end of string
assert(section.src = 'foo.bar("%>").baz');

Delimiters are ignored if they are inside strings or comments.

API

parse(str, state = defaultState(), options = {start: 0, end: src.length})

Parse a string starting at the index start, and return the state after parsing that string.

If you want to parse one string in multiple sections you should keep passing the resulting state to the next parse operation.

Returns a State object.

parseMax(src, options = {start: 0})

Parses the source until the first unmatched close bracket (any of ), }, ]). It returns an object with the structure:

{
  start: 0,//index of first character of string
  end: 13,//index of first character after the end of string
  src: 'source string'
}

parseUntil(src, delimiter, options = {start: 0, includeLineComment: false})

Parses the source until the first occurence of delimiter which is not in a string or a comment. If includeLineComment is true, it will still count if the delimiter occurs in a line comment, but not in a block comment. It returns an object with the structure:

{
  start: 0,//index of first character of string
  end: 13,//index of first character after the end of string
  src: 'source string'
}

parseChar(character, state = defaultState())

Parses the single character and returns the state. See parse for the structure of the returned state object. N.B. character must be a single character not a multi character string.

defaultState()

Get a default starting state.

isPunctuator(character)

Returns true if character represents punctuation in JavaScript.

isKeyword(name)

Returns true if name is a keyword in JavaScript.

State

A state is an object with the following structure

{
  lineComment: false, //true if inside a line comment
  blockComment: false, //true if inside a block comment

  singleQuote: false, //true if inside a single quoted string
  doubleQuote: false, //true if inside a double quoted string
  regexp:      false, //true if inside a regular expression
  escaped: false, //true if in a string and the last character was an escape character

  roundDepth: 0, //number of un-closed open `(` brackets
  curlyDepth: 0, //number of un-closed open `{` brackets
  squareDepth: 0 //number of un-closed open `[` brackets
}

It also has the following useful methods:

• .isString() returns true if the current location is inside a string.
• .isComment() returns true if the current location is inside a comment.
• isNesting() returns true if the current location is anything but at the top level, i.e. with no nesting.

License

MIT