fixes #471 (#745)

* checks if RegExp[Symbol.replace] substitutes undefined capture groups

* use wellKnownSymbol util to get symbol key for replace method

* fixes REGEXP_REPLACE_SUBSTITUTES_UNDEFINED_CAPTURE conditional logic

* caches Symbol.replace as constant, uses regexp literal, swaps default for guard in fix-regexp-well-known-symbol-logic

packages/core-js/internals/fix-regexp-well-known-symbol-logic.js

@@ -28,6 +28,15 @@ var REPLACE_KEEPS_$0 = (function () {
   return 'a'.replace(/./, '$0') === '$0';
 })();
 
+var REPLACE = wellKnownSymbol('replace');
+// Safari <= 13.0.3(?) substitutes nth capture where n>m with an empty string
+var REGEXP_REPLACE_SUBSTITUTES_UNDEFINED_CAPTURE = (function () {
+  if (/./[REPLACE]) {
+    return /./[REPLACE]('a', '$0') === '';
+  }
+  return false;
+})();
+
 // Chrome 51 has a buggy "split" implementation when RegExp#exec !== nativeExec
 // Weex JS has frozen built-in prototypes, so use try / catch wrapper
 var SPLIT_WORKS_WITH_OVERWRITTEN_EXEC = !fails(function () {
@@ -75,7 +84,11 @@ module.exports = function (KEY, length, exec, sham) {
   if (
     !DELEGATES_TO_SYMBOL ||
     !DELEGATES_TO_EXEC ||
-    (KEY === 'replace' && !(REPLACE_SUPPORTS_NAMED_GROUPS && REPLACE_KEEPS_$0)) ||
+    (KEY === 'replace' && !(
+      REPLACE_SUPPORTS_NAMED_GROUPS &&
+      REPLACE_KEEPS_$0 &&
+      REGEXP_REPLACE_SUBSTITUTES_UNDEFINED_CAPTURE
+    )) ||
     (KEY === 'split' && !SPLIT_WORKS_WITH_OVERWRITTEN_EXEC)
   ) {
     var nativeRegExpMethod = /./[SYMBOL];
@@ -90,7 +103,10 @@ module.exports = function (KEY, length, exec, sham) {
         return { done: true, value: nativeMethod.call(str, regexp, arg2) };
       }
       return { done: false };
-    }, { REPLACE_KEEPS_$0: REPLACE_KEEPS_$0 });
+    }, {
+      REPLACE_KEEPS_$0: REPLACE_KEEPS_$0,
+      REGEXP_REPLACE_SUBSTITUTES_UNDEFINED_CAPTURE: REGEXP_REPLACE_SUBSTITUTES_UNDEFINED_CAPTURE
+    });
     var stringMethod = methods[0];
     var regexMethod = methods[1];
 

packages/core-js/modules/es.string.replace.js

@@ -33,7 +33,10 @@ fixRegExpWellKnownSymbolLogic('replace', 2, function (REPLACE, nativeReplace, ma
     // `RegExp.prototype[@@replace]` method
     // https://tc39.github.io/ecma262/#sec-regexp.prototype-@@replace
     function (regexp, replaceValue) {
-      if (reason.REPLACE_KEEPS_$0 || (typeof replaceValue === 'string' && replaceValue.indexOf('$0') === -1)) {
+      if (
+        !reason.REGEXP_REPLACE_SUBSTITUTES_UNDEFINED_CAPTURE &&
+        (reason.REPLACE_KEEPS_$0 || (typeof replaceValue === 'string' && replaceValue.indexOf('$0') === -1))
+      ) {
         var res = maybeCallNative(nativeReplace, regexp, this, replaceValue);
         if (res.done) return res.value;
       }