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

Parsing

Work out how much depth changes:

var state = parse('foo(arg1, arg2, {\n  foo: [a, b\n');
assert.deepEqual(state.stack, [')', '}', ']']);

parse('    c, d]\n  })', state);
assert.deepEqual(state.stack, []);

Custom Delimited Expressions

Find code up to a custom delimiter:

// EJS-style
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');

// Jade-style
var section = parser.parseUntil('#[p= [1, 2][i]]', ']', {start: 2})
assert(section.start === 2);
assert(section.end === 14); // exclusive end of string
assert(section.src === 'p= [1, 2][i]')

// Dumb parsing
// Stop at first delimiter encountered, doesn't matter if it's nested or not
// This is the character-parser@1 default behavior.
var section = parser.parseUntil('#[p= [1, 2][i]]', '}', {start: 2, ignoreNesting: true})
assert(section.start === 2);
assert(section.end === 10); // exclusive end of string
assert(section.src === 'p= [1, 2')
''

Delimiters are ignored if they are inside strings or comments.

API

All methods may throw an exception in the case of syntax errors. The exception contains an additional code property that always starts with CHARACTER_PARSER: that is unique for the error.

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.

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

Parses the source until the first occurrence of delimiter which is not in a string or a comment.

If ignoreLineComment is true, it will still count if the delimiter occurs in a line comment.

If ignoreNesting is true, it will stop at the first bracket, not taking into account if the bracket part of nesting or not. See example above.

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.

TOKEN_TYPES & BRACKETS

Objects whose values can be a frame in the stack property of a State (documented below).

State

A state is an object with the following structure

{
  stack: [],          // stack of detected brackets; the outermost is [0]
  regexpStart: false, // true if a slash is just encountered and a REGEXP state has just been added to the stack

  escaped: false,     // true if in a string and the last character was an escape character
  hasDollar: false,   // true if in a template string and the last character was a dollar sign

  src: '',            // the concatenated source string
  history: '',        // reversed `src`
  lastChar: ''        // last parsed character
}

stack property can contain any of the following:

• Any of the property values of characterParser.TOKEN_TYPES
• Any of the property values of characterParser.BRACKETS (the end bracket, not the starting bracket)

It also has the following useful methods:

• .current() returns the innermost bracket (i.e. the last stack frame).
• .isString() returns true if the current location is inside a string.
• .isComment() returns true if the current location is inside a comment.
• .isNesting([opts]) returns true if the current location is not at the top level, i.e. if the stack is not empty. If opts.ignoreLineComment is true, line comments are not counted as a level, so for // a it will still return false.

Errors

All errors thrown by character-parser has a code property attached to it that allows one to identify what sort of error is thrown. For errors thrown from parse and parseUntil, an additional index property is available.

Transition from v1

In character-parser@2, we have changed the APIs quite a bit. These are some notes that will help you transition to the new version.

State Object Changes

Instead of keeping depths of different brackets, we are now keeping a stack. We also removed some properties:

state.lineComment  → state.current() === parser.TOKEN_TYPES.LINE_COMMENT
state.blockComment → state.current() === parser.TOKEN_TYPES.BLOCK_COMMENT
state.singleQuote  → state.current() === parser.TOKEN_TYPES.SINGLE_QUOTE
state.doubleQuote  → state.current() === parser.TOKEN_TYPES.DOUBLE_QUOTE
state.regexp       → state.current() === parser.TOKEN_TYPES.REGEXP

parseMax

This function has been removed since the usefulness of this function has been questioned. You should find that parseUntil is a better choice for your task.

parseUntil

The default behavior when the delimiter is a bracket has been changed so that nesting is taken into account to determine if the end is reached.

To preserve the original behavior, pass ignoreNesting: true as an option.

To see the difference between the new and old behaviors, see the "Usage" section earlier.

parseMaxBracket

This function has been merged into parseUntil. You can directly rename the function call without any repercussions.

License

MIT