Regular Expression

Static Semantics: IsValidRegularExpressionLiteral(literal):

function IsValidRegularExpressionLiteral(literal) {
   // 1. Let flags be the FlagText of literal.
   const flags = literal.flags;
   // 2. If flags contains any code points other than d, g, i, m, s, u, v, or y, or if flags contains any code point more than once, return false.
   const validFlags = new Set(['d', 'g', 'i', 'm', 's', 'u', 'v', 'y']);
   let flagsSet = new Set();
   for (const flag of flags) {
     if (!validFlags.has(flag) || flagsSet.has(flag)) return false;
     flagsSet.add(flag);
   }
   // 3. If flags contains u, let u be true; else let u be false.
   const u = flags.includes('u');
   // 4. If flags contains v, let v be true; else let v be false.
   const v = flags.includes('v');
   // 5. Let patternText be the BodyText of literal.
   let patternText = literal.source;
   // 6. If u is false and v is false, process patternText.
   if (!u && !v) {
     // 6.1 Let stringValue be CodePointsToString(patternText).
     const stringValue = String.fromCodePoint(...patternText);
     // 6.2 Set patternText to the sequence of code points resulting from interpreting each of the 16-bit elements of stringValue as a Unicode BMP code point. UTF-16 decoding is not applied to the elements.
     patternText = [...stringValue].map(char => char.codePointAt(0));
   }
   // 7. Let pattern be the ParseText(stringValue, u, v).
   let parseResult;
   try {
     parseResult = RegExp(patternText, flags);
     parseResult = true;
   } catch (e) {
     parseResult = false;
   }
   return parseResult;
 }