Add String.replaceFirstMapped.

sdk/lib/_internal/compiler/js_lib/string_helper.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of _js_helper;
 
 class StringMatch implements Match {
   const StringMatch(int this.start,
                     String this.input,
                     String this.pattern);
@@ skipping 175 matching lines @@
     }
     buffer.write(onNonMatch(receiver.substring(startIndex, position)));
     buffer.write(onMatch(new StringMatch(position, receiver, pattern)));
     startIndex = position + patternLength;
   }
   buffer.write(onNonMatch(receiver.substring(startIndex)));
   return buffer.toString();
 }
 
 
-stringReplaceFirstUnchecked(receiver, from, to, [int startIndex = 0]) {
+stringReplaceFirstUnchecked(receiver, from, to, int startIndex) {
   if (from is String) {
     var index = receiver.indexOf(from, startIndex);

[floitsch, 2015/02/11 11:49:14]

we are missing types here... (and in your code).

[Lasse Reichstein Nielsen, 2015/02/12 09:17:16]

Added.
You are also missing types on all the function signatures, so I assumed it was
deliberate.

     if (index < 0) return receiver;
     return '${receiver.substring(0, index)}$to'
            '${receiver.substring(index + from.length)}';
-  } else if (from is JSSyntaxRegExp) {
+  }
+  if (from is JSSyntaxRegExp) {
     return startIndex == 0 ?
         stringReplaceJS(receiver, regExpGetNative(from), to) :
         stringReplaceFirstRE(receiver, from, to, startIndex);
-  } else {
-    checkNull(from);
-    // TODO(floitsch): implement generic String.replace (with patterns).
-    throw "String.replace(Pattern) UNIMPLEMENTED";
   }
+  checkNull(from);
+  var matches = from.allMatches(receiver, startIndex).iterator;
+  if (!matches.moveNext()) return receiver;
+  var match = matches.current;
+  return '${receiver.substring(0, match.start)}$to'
+         '${receiver.substring(match.end)}';
+}
+
+stringReplaceFirstMappedUnchecked(receiver, from, replace,
+                                  int startIndex) {
+  var matches = from.allMatches(receiver, startIndex).iterator;
+  if (!matches.moveNext()) return receiver;
+  var match = matches.current;
+  var replacement = "${replace(match)}";
+  return '${receiver.substring(0, match.start)}$replacement'
+         '${receiver.substring(match.end)}';
 }
 
 stringJoinUnchecked(array, separator) {
   return JS('String', r'#.join(#)', array, separator);
 }