@technobuddha/library/src/unescape-java.ts

A large library of useful functions

import { empty } from './unicode.ts';

// cspell:ignore unnnn
/**
 * Unescape a string encoded in Java style
 *
 * | Escape Sequence    | Hex                  | Character                |
 * | ------------------ | -------------------- | ------------------------ |
 * | \\b                | 0x08                 | Backspace                |
 * | \\f                | 0x0c                 | Form Feed                |
 * | \\n                | 0x0a                 | New Line                 |
 * | \\r                | 0x0d                 | Carriage Return          |
 * | \\t                | 0x09                 | Tab                      |
 * | \\\\               | 0x5c                 | Backslash                |
 * | \\'                | 0x27                 | Single Quote             |
 * | \\"                | 0x22                 | Double Quote             |
 * | \\unnnn            | 0x0000-0xFFFF    | Unicode Escape           |
 * @param input - The string to unescape
 * @returns the string with escapes resolved
 * @example
 * ```typescript
 * unescapeJava('Hello\\nWorld'); // "Hello\nWorld"
 * unescapeJava('\\u20ac'); // "€"
 * unescapeJava('\\tTabbed'); // "\tTabbed"
 * unescapeJava('\\\\'); // "\\"
 * ```
 * @group Programming
 * @category Escaping
 */
export function unescapeJava(input: string): string {
  // cspell:ignore bfnrt
  return input.replaceAll(/\\(([bfnrt"'\\])|([0-7]{1,3})|(u+[0-9a-fA-F]{4}))/gu, (escape) => {
    const c = escape.charAt(1);

    if (c === 'b') {
      return '\b';
    }
    if (c === 'f') {
      return '\f';
    }
    if (c === 'n') {
      return '\n';
    }
    if (c === 'r') {
      return '\r';
    }
    if (c === 't') {
      return '\t';
    }
    if (c >= '0' && c <= '7') {
      // eslint-disable-next-line unicorn/prefer-code-point
      return String.fromCharCode(Number.parseInt(escape.slice(1), 8));
    }
    if (c === 'u') {
      // Java allows multiple occurrences of 'u' in it's escape sequence

      // eslint-disable-next-line unicorn/prefer-code-point
      return String.fromCharCode(Number.parseInt(escape.replace(/^u+/u, empty), 16));
    }

    return escape.slice(1);
  });
}