Implemented String.prototype.repeat as per ES6 draft 07-15-13, section 15.5.3.21

src/string.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 864 matching lines @@
   var two_byte = %NewString(n - i, NEW_TWO_BYTE_STRING);
   for (var j = 0; i < n; i++, j++) {
     var code = %_Arguments(i);
     if (!%_IsSmi(code)) code = ToNumber(code) & 0xffff;
     %_TwoByteSeqStringSetChar(two_byte, j, code);
   }
   return one_byte + two_byte;
 }
 
 
+// ES6 draft 07-15-13, section 15.5.3.21
+function StringRepeat(count) {
+  if (IS_NULL_OR_UNDEFINED(this) && !IS_UNDETECTABLE(this)) {
+    throw MakeTypeError("called_on_null_or_undefined",
+                        ["String.prototype.repeat"]);
+  }
+

[Sven Panne, 2013/07/29 13:27:53]

We have to call TO_STRING_INLINE here, not later, because this is observable.
Please add a test case for this, too.

+  if (IS_NULL_OR_UNDEFINED(count) && !IS_UNDETECTABLE(count)) {

[Sven Panne, 2013/07/29 13:27:53]

Why test this? What should really happen at that point is ToInteger(count),
which is observable. Again: Test case!

+    throw MakeTypeError("called_on_null_or_undefined",
+                        ["String.prototype.repeat"]);
+  }
+
+  var s = TO_STRING_INLINE(this);
+  if (s.length === 0) {

[Sven Panne, 2013/07/29 13:27:53]

This optimization is not allowed by the spec, at least not if something
observable comes after it in the final implementation.

+    return s;
+  }
+
+  var n = ToNumber(count);
+  if (NUMBER_IS_NAN(n) || n < 0 || !NUMBER_IS_FINITE(n)) {
+    throw MakeRangeError("invalid_count_value", []);
+  }
+
+  n = TO_INTEGER(n);
+  if (n === 0) {

[Sven Panne, 2013/07/29 13:27:53]

I am not sure if a zero count is a common case, we should probably remove that.

+    return "";
+  }
+
+  var elements = new InternalArray(n);
+  var i = 0;

[Sven Panne, 2013/07/29 13:27:53]

Style nit: Use a for loop for readability.

+  while (i < n) {
+    elements[i++] = s;
+  }
+
+  return %StringBuilderConcat(elements, n, "");
+}
+
+
 // Helper function for very basic XSS protection.
 function HtmlEscape(str) {
   return TO_STRING_INLINE(str).replace(/</g, "&lt;")
                               .replace(/>/g, "&gt;")
                               .replace(/"/g, "&quot;")
                               .replace(/'/g, "&#039;");
 }
 
 
 // Compatibility support for KJS.
@@ skipping 108 matching lines @@
     "fontcolor", StringFontcolor,
     "fontsize", StringFontsize,
     "big", StringBig,
     "blink", StringBlink,
     "bold", StringBold,
     "fixed", StringFixed,
     "italics", StringItalics,
     "small", StringSmall,
     "strike", StringStrike,
     "sub", StringSub,
-    "sup", StringSup
+    "sup", StringSup,
+    "repeat", StringRepeat
   ));
 }
 
 SetUpString();