Optimize String.prototype.includes

src/string.js

Index: src/string.js
diff --git a/src/string.js b/src/string.js
index 3ddd6d26cedfd9e49a5e624e071f0caeb005fba7..bf1af700b8cd711a354ecc8e9085b06812cc4f3c 100644
--- a/src/string.js
+++ b/src/string.js
@@ -1031,27 +1031,29 @@ function StringEndsWith(searchString /* position */) {  // length == 1
 function StringIncludes(searchString /* position */) {  // length == 1
   CHECK_OBJECT_COERCIBLE(this, "String.prototype.includes");
 
-  var s = TO_STRING_INLINE(this);
+  var string = TO_STRING_INLINE(this);
 
   if (IS_REGEXP(searchString)) {
     throw MakeTypeError(kFirstArgumentNotRegExp, "String.prototype.includes");
   }
 
-  var ss = TO_STRING_INLINE(searchString);
+  var searchString = TO_STRING_INLINE(searchString);

[adamk, 2015/07/14 23:24:55]

No need for "var" here, you're re-assigning a parameter now.

[Dan Ehrenberg, 2015/07/14 23:45:48]

Done.

   var pos = 0;
   if (%_ArgumentsLength() > 1) {
     pos = %_Arguments(1);  // position
     pos = $toInteger(pos);

[adamk, 2015/07/14 23:24:55]

TO_INTEGER here for more performance

[Dan Ehrenberg, 2015/07/14 23:45:48]

This doesn't affect my benchmark because %_ArgumentsLength() == 1, but I made
the change for consistency.

   }
 
-  var s_len = s.length;
-  var start = MathMin(MathMax(pos, 0), s_len);
-  var ss_len = ss.length;
-  if (ss_len + start > s_len) {
+  var stringLength = string.length;
+  if (pos < 0) pos = 0;
+  if (pos > stringLength) pos = stringLength;
+  var searchStringLength = searchStringLength.length;
+
+  if (searchStringLength + pos > stringLength) {
     return false;
   }
 
-  return %StringIndexOf(s, ss, start) !== -1;
+  return %StringIndexOf(string, searchString, pos) !== -1;
 }