Regex Builder Prototype

re_builder_prototype.js

//== RE::ASSERTIONS ============================================================
const WORD_BOUNDARY = String.raw`\b`;

function lookahead(x, y) {
  const symbol = "?=";
  return x + group(symbol + y);
}

function lookbehind(x, y) {
  const symbol = "?<=";
  return group(symbol + y) + x;
}

//== RE::CHARACTOR_CLASSES =====================================================
const ALL_CHAR = ".";
const NUM = String.raw`\d`;
const SPACE = String.raw`\s`;

//== RE::GROUP =================================================================
function group(str) {
  return "(" + str + ")";
}

function or(...strs) {
  return group(strs.join('|'));
}

//== RE::QUANTIFIERS ===========================================================
function count(str, length) {
  return str + `{${length}}`;
}

function infinity(str) {
  return str + "*";
}

function lazy(str) {
  return str + "?";
}

function maybe(str) {
  return lazy(group(str));
}

//== RE::CONST =================================================================
const ALL = infinity(ALL_CHAR);

//== DATA ======================================================================
const MONTH_ARR = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"];

// Date
const MONTH = or(...MONTH_ARR);
const DAY   = NUM + lazy(NUM);
const YEAR  = count(NUM, 4);

// Date Group
const MONTH_DAY  = group(MONTH + SPACE + DAY + WORD_BOUNDARY);
const SPACE_YEAR = group(WORD_BOUNDARY + SPACE + YEAR);

// Check
// Before(Not cleanup), const MD_EXIST = maybe(lookahead(MONTH_DAY, lookahead(ALL, SPACE_YEAR)));
// Before(Not cleanup), const SY_EXIST = maybe(lookbehind(SPACE_YEAR, lookahead(MONTH_DAY, "") + ALL));
const MD_EXIST = maybe(lookahead(MONTH_DAY, ALL + SPACE_YEAR));
const SY_EXIST = maybe(lookbehind(SPACE_YEAR, MONTH_DAY + ALL));
const result = RegExp(MD_EXIST + SY_EXIST, "gm");

//== RESULT ====================================================================
console.log(result);
// => /(((Jan|Feb|Mar|Apr|Jun|Jul|Aug|Sep|Oct|Nov|Dec)\s\d\d?\b)(?=.*(\b\s\d{4})))?((?<=((Jan|Feb|Mar|Apr|Jun|Jul|Aug|Sep|Oct|Nov|Dec)\s\d\d?\b).*)(\b\s\d{4}))?/gm
// https://regexr.com/65dfm

// Before Result
// => /(((Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec)\s\d\d?\b)(?=.*(?=\b\s\d{4})))?((?<=(?=(Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec)\s\d\d?\b).*)\b\s\d{4})?/gm
// https://regexr.com/65d56

Contexts

• https://gall.dcinside.com/mgallery/board/view/?id=github&no=24655
• https://gall.dcinside.com/mgallery/board/view/?id=github&no=24658
• https://gall.dcinside.com/mgallery/board/view/?id=github&no=24829
• https://gall.dcinside.com/mgallery/board/view/?id=github&no=24850
• https://gall.dcinside.com/mgallery/board/view/?id=github&no=24858