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

src/string.js

Index: src/string.js
diff --git a/src/string.js b/src/string.js
index cb82c166346fc7ba5491a1e9e5d28e0e9b5a5108..96d68e249fe5749fa8ef2500e5694555c1122340 100644
--- a/src/string.js
+++ b/src/string.js
@@ -882,6 +882,43 @@ function StringFromCharCode(code) {
 }
 
 
+// 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;")
@@ -1010,7 +1047,8 @@ function SetUpString() {
     "small", StringSmall,
     "strike", StringStrike,
     "sub", StringSub,
-    "sup", StringSup
+    "sup", StringSup,
+    "repeat", StringRepeat
   ));
 }