JS: Re-added comment, moved surrogates code to the right place

js/binary/decoder.js

@@ -941,7 +941,8 @@ jspb.BinaryDecoder.prototype.readString = function(length) {
       codeUnits.push(high, low)
     }
   }
-
+  // String.fromCharCode.apply is faster than manually appending characters on
+  // Chrome 25+, and generates no additional cons string garbage.
   var result = String.fromCharCode.apply(null, codeUnits);
   this.cursor_ = cursor;
   return result;

js/binary/encoder.js

@@ -413,6 +413,13 @@ jspb.BinaryEncoder.prototype.writeString = function(value) {
   for (var i = 0; i < value.length; i++) {
     
     var c = value.charCodeAt(i);
+
+    if (c < 128) {
+      this.buffer_.push(c);
+    } else if (c < 2048) {
+      this.buffer_.push((c >> 6) | 192);
+      this.buffer_.push((c & 63) | 128);
+    } else if (c < 65536) {
       // Look for surrogates
       if (c >= 0xD800 && c <= 0xDBFF && i + 1 < value.length) {
         var second = value.charCodeAt(i + 1);
@@ -421,13 +428,6 @@ jspb.BinaryEncoder.prototype.writeString = function(value) {
           c = (c - 0xD800) * 0x400 + second - 0xDC00 + 0x10000;
         }
       }
-
-    if (c < 128) {
-      this.buffer_.push(c);
-    } else if (c < 2048) {
-      this.buffer_.push((c >> 6) | 192);
-      this.buffer_.push((c & 63) | 128);
-    } else if (c < 65536) {
       this.buffer_.push((c >> 12) | 224);
       this.buffer_.push(((c >> 6) & 63) | 128);
       this.buffer_.push((c & 63) | 128);