RegExp#escape.mts

const SYNTAX_CHARACTER = "\\^$\\\\.*+?()[\\]{}|/";
const TABLE_67_CHARACTER = "\\t\\n\\v\\f\\r";
const OTHER_PUNCTUATORS_CHARACTER = ",\\-=<>#&!%:;@~\\'\\\"\\`";
const WHITE_SPACE_CHARACTER =
  "\\t\\v\\f\\uFEFF \\u00A0\\u1680\\u2000\\u2001\\u2002\\u2003\\u2004\\u2005\\u2006\\u2007\\u2008\\u2009\\u200A\\u202F\\u205F\\u3000";
const LINE_TERMINATOR_CHARACTER = "\\n\\r\\u2028\\u2029";
const MATCH_MALFORMED_LEADING_SURROGATE =
  "[\\uD800-\\uDBFF](?![\\uDC00-\\uDFFF])";
const MATCH_MALFORMED_TRAILING_SURROGATE =
  "(?<![\\uD800-\\uDBFF])[\\uDC00-\\uDFFF]";

const matchFirstAlphanumeric = /^[A-Za-z0-9]/;

const findNextEscape = new RegExp(`[${SYNTAX_CHARACTER}]`, "g");
const findNextEncode = new RegExp(
  `[${TABLE_67_CHARACTER}${OTHER_PUNCTUATORS_CHARACTER}${WHITE_SPACE_CHARACTER}${LINE_TERMINATOR_CHARACTER}]|${MATCH_MALFORMED_LEADING_SURROGATE}|${MATCH_MALFORMED_TRAILING_SURROGATE}`,
  "g"
);

function RegExp_escape(S: string) {
  if (typeof S !== "string") throw new TypeError("Argument is not a string");

  let cursor;
  let accumulator;

  // Handle special case for an alphanumeric first character
  // and initialize the cursor and accumulator
  if (matchFirstAlphanumeric.test(S)) {
    cursor = 1;
    accumulator = "\\x" + S.charCodeAt(0).toString(16);
  } else {
    cursor = 0;
    accumulator = "";
  }

  // Find the first escapable character or encoable character
  let hasNextEscape = findNextEscape.test(S);
  let hasNextEncode = findNextEncode.test(S);
  for (;;) {
    const escapeIndex = findNextEscape.lastIndex;
    const encodeIndex = findNextEncode.lastIndex;

    // Do escape or encode depending on which match is closer
    if (hasNextEscape && (!hasNextEncode || escapeIndex < encodeIndex)) {
      accumulator += S.slice(cursor, escapeIndex - 1) + "\\";
      cursor = escapeIndex - 1;

      hasNextEscape = findNextEscape.test(S);
    } else if (hasNextEncode && (!hasNextEscape || encodeIndex < escapeIndex)) {
      const code = S.charCodeAt(encodeIndex - 1);
      const slice = S.slice(cursor, encodeIndex - 1);
      cursor = encodeIndex;

      switch (code) {
        case 0x09:
          accumulator += slice + "\\t";
          break;
        case 0x0a:
          accumulator += slice + "\\n";
          break;
        case 0x0b:
          accumulator += slice + "\\v";
          break;
        case 0x0c:
          accumulator += slice + "\\f";
          break;
        case 0x0d:
          accumulator += slice + "\\r";
          break;
        default:
          const hex = code.toString(16);
          accumulator += slice + (code <= 0xff ? "\\x" : "\\u") + hex;
      }

      hasNextEncode = findNextEncode.test(S);
    } else {
      return accumulator + S.slice(cursor);
    }
  }
}