multiconf/lib/jsonc-parser.js

Work with JSON configs

/**
 * JSONC Parser class for handling JSON with comments
 */
class JSONCParser {
  /**
   * Parse JSONC string to object.
   * @param {string} jsoncString JSONC string to parse.
   * @returns {object} Parsed object.
   * @throws {SyntaxError} If the JSONC string is invalid.
   */
  static parse(jsoncString) {
    if (typeof jsoncString !== 'string') {
      throw new TypeError('Input must be a string');
    }

    // Remove comments and trailing commas.
    const jsonString = this._removeComments(jsoncString);
    return JSON.parse(jsonString);
  }

  /**
   * Remove comments and trailing commas from JSONC string.
   * @param {string} jsoncString JSONC string to clean.
   * @returns {string} Clean JSON string.
   * @private
   */
  static _removeComments(jsoncString) {
    let result = '';
    let inString = false;
    let inSingleLineComment = false;
    let inMultiLineComment = false;
    let lastChar = '';
    let commentDepth = 0;
    let escapeNext = false;

    for (let i = 0; i < jsoncString.length; i++) {
      const char = jsoncString[i];
      const nextChar = jsoncString[i + 1];

      // Handle escape sequences.
      if (char === '\\' && !escapeNext) {
        escapeNext = true;
        result += char;
        continue;
      }

      // Handle string literals.
      if (char === '"' && !escapeNext) {
        inString = !inString;
      }

      // Handle single-line comments.
      if (!inString && char === '/' && nextChar === '/') {
        inSingleLineComment = true;
        i++; // Skip next character.
        continue;
      }

      // Handle multi-line comments.
      if (!inString && char === '/' && nextChar === '*') {
        inMultiLineComment = true;
        commentDepth++;
        i++; // Skip next character.
        continue;
      }

      // End single-line comment.
      if (inSingleLineComment && (char === '\n' || char === '\r')) {
        inSingleLineComment = false;
      }

      // Handle nested multi-line comments.
      if (inMultiLineComment) {
        if (char === '*' && nextChar === '/') {
          commentDepth--;
          if (commentDepth === 0) {
            inMultiLineComment = false;
          }
          i++; // Skip next character.
          continue;
        }
        if (char === '/' && nextChar === '*') {
          commentDepth++;
          i++; // Skip next character.
          continue;
        }
        continue;
      }

      // Only add characters that are not in comments.
      if (!inSingleLineComment && !inMultiLineComment) {
        // Handle trailing commas.
        if (char === ',' && !inString) {
          // Look ahead to find the next non-whitespace character.
          let j = i + 1;
          let foundNonWhitespace = false;

          while (j < jsoncString.length) {
            const nextChar = jsoncString[j];

            // Skip over whitespace.
            if (nextChar === ' ' || nextChar === '\t' || 
                nextChar === '\n' || nextChar === '\r') {
              j++;
              continue;
            }

            // Skip multiple commas (keep only one).
            if (nextChar === ',') {
              j++;
              continue;
            }

            // If the next non-whitespace character is a closing bracket/brace, skip the comma.
            if (nextChar === '}' || nextChar === ']') {
              foundNonWhitespace = true;
              break;
            }

            // Otherwise, this is a valid comma.
            foundNonWhitespace = true;
            result += char;
            break;
          }

          // If we reached the end of the string or only found closing brackets, don't add the comma.
          if (!foundNonWhitespace) {
            // Do nothing - skip the comma.
          }
        } else {
          result += char;
        }
      }

      lastChar = char;
      escapeNext = false;
    }

    // Validate that all comments are properly closed.
    if (inMultiLineComment) {
      throw new SyntaxError('Unclosed multi-line comment');
    }

    return result;
  }
}

// Export.
module.exports = JSONCParser;