[es6] implement Array.prototype.copyWithin()

src/harmony-array.js

Index: src/harmony-array.js
diff --git a/src/harmony-array.js b/src/harmony-array.js
index dbcb292a0876842e8d3a6d4c0d21d997cdf6d977..62974793c5f0c6689a6aa20aa18de773c6d13426 100644
--- a/src/harmony-array.js
+++ b/src/harmony-array.js
@@ -10,6 +10,72 @@
 
 // -------------------------------------------------------------------
 
+// ES6 draft 05-22-14, section 22.1.3.3
+function ArrayCopyWithin(target, start /* [ , end ] */ ) { // length == 2

[adamk, 2015/04/17 22:34:17]

Another option here is to name the argument and use %FunctionSetLength down
below to get the length right. Seems like that's more common elsewhere, while
this file prefers this style.

[caitp (gmail), 2015/04/18 04:50:29]

Done, I prefer the %FunctionSetLength() approach

+  CHECK_OBJECT_COERCIBLE(this, "Array.prototype.copyWithin");
+
+  var array = ToObject(this);

[adamk, 2015/04/17 22:34:16]

TO_OBJECT_INLINE

[caitp (gmail), 2015/04/18 04:50:29]

Done.

+  var length = ToInteger(array.length);

[adamk, 2015/04/17 22:34:17]

TO_UINT32 (hmm, we should figure out this ToLength stuff at some point).

[caitp (gmail), 2015/04/18 04:50:30]

We've had ToLength() for a while --- not sure how inline-able it is, but it
should be doable. Went with that

+  var to;
+  var from;
+  var relativeEnd = length;

[adamk, 2015/04/17 22:34:16]

I'd move this down to its initialization to make it clear that it gets the right
value. I'd prefer the rest move down, too, to just before their initialization.

[caitp (gmail), 2015/04/18 04:50:29]

Done.

+  var end;
+  var final;
+  var count;
+  var direction = 1;

[adamk, 2015/04/17 22:34:16]

Same here, moving this down will make it clearer I think.

[caitp (gmail), 2015/04/18 04:50:30]

Done.

+  var fromVal;
+
+  target = ToInteger(target);

[adamk, 2015/04/17 22:34:17]

TO_INTEGER (and similar below)

[caitp (gmail), 2015/04/18 04:50:30]

Done.

+  if (target < 0) {
+    to = MathMax(length + target, 0);

[adamk, 2015/04/17 22:34:17]

I think this is now spelled $max()

[caitp (gmail), 2015/04/18 04:50:29]

Done.

+  } else {
+    to = MathMin(target, length);

[adamk, 2015/04/17 22:34:17]

and this is $min()

[caitp (gmail), 2015/04/18 04:50:29]

Done.

+  }
+
+  start = ToInteger(start);
+
+  if (start < 0) {
+    from = MathMax(length + start, 0);
+  } else {
+    from = MathMin(start, length);
+  }
+
+  if (%_ArgumentsLength() > 2) {
+    end = %_Arguments(2);
+    if (!IS_UNDEFINED(end)) {
+      relativeEnd = ToInteger(end);
+    }
+  }
+
+  if (relativeEnd < 0) {
+    final = MathMax(length + relativeEnd, 0);
+  } else {
+    final = MathMin(relativeEnd, length);
+  }
+
+  count = MathMin(final - from, length - to);
+
+  if (from < to && to < (from + count)) {
+    direction = -1;
+    from = from + count - 1;
+    to = to + count - 1;
+  }
+
+  while (count > 0) {
+    if (from in array) {
+      fromVal = array[from];
+      array[to] = fromVal;
+    } else {
+      delete array[to];
+    }
+    from = from + direction;
+    to = to + direction;
+    count--;
+  }
+
+  return array;
+}
+
 // ES6 draft 07-15-13, section 15.4.3.23
 function ArrayFind(predicate /* thisArg */) {  // length == 1
   CHECK_OBJECT_COERCIBLE(this, "Array.prototype.find");
@@ -130,6 +196,7 @@ function HarmonyArrayExtendArrayPrototype() {
 
   // Set up the non-enumerable functions on the Array prototype object.
   InstallFunctions($Array.prototype, DONT_ENUM, $Array(
+    "copyWithin", ArrayCopyWithin,
     "find", ArrayFind,
     "findIndex", ArrayFindIndex,
     "fill", ArrayFill