querystring: improve escape() performance

This commit improves escape() performance by up to 15% with the
existing querystring-stringify benchmarks by reducing the number
of string concatentations. A potential deopt is also avoided by
making sure the index passed to charCodeAt() is within bounds.

PR-URL: #5012
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

benchmark/querystring/querystring-stringify.js

@@ -4,7 +4,7 @@ var v8 = require('v8');
 
 var bench = common.createBenchmark(main, {
   type: ['noencode', 'encodemany', 'encodelast'],
-  n: [1e6],
+  n: [1e7],
 });
 
 function main(conf) {
@@ -37,6 +37,7 @@ function main(conf) {
 
   v8.setFlagsFromString('--allow_natives_syntax');
   eval('%OptimizeFunctionOnNextCall(querystring.stringify)');
+  querystring.stringify(input);
 
   bench.start();
   for (var i = 0; i < n; i += 1)

lib/querystring.js

@@ -90,16 +90,13 @@ for (var i = 0; i < 256; ++i)
 QueryString.escape = function(str) {
   // replaces encodeURIComponent
   // http://www.ecma-international.org/ecma-262/5.1/#sec-15.1.3.4
-  str = '' + str;
-  var len = str.length;
+  if (typeof str !== 'string')
+    str += '';
   var out = '';
-  var i, c;
-
-  if (len === 0)
-    return str;
+  var lastPos = 0;
 
-  for (i = 0; i < len; ++i) {
-    c = str.charCodeAt(i);
+  for (var i = 0; i < str.length; ++i) {
+    var c = str.charCodeAt(i);
 
     // These characters do not need escaping (in order):
     // ! - . _ ~
@@ -112,35 +109,50 @@ QueryString.escape = function(str) {
         (c >= 0x30 && c <= 0x39) ||
         (c >= 0x41 && c <= 0x5A) ||
         (c >= 0x61 && c <= 0x7A)) {
-      out += str[i];
       continue;
     }
 
+    if (i - lastPos > 0)
+      out += str.slice(lastPos, i);
+
     // Other ASCII characters
     if (c < 0x80) {
+      lastPos = i + 1;
       out += hexTable[c];
       continue;
     }
 
     // Multi-byte characters ...
     if (c < 0x800) {
+      lastPos = i + 1;
       out += hexTable[0xC0 | (c >> 6)] + hexTable[0x80 | (c & 0x3F)];
       continue;
     }
     if (c < 0xD800 || c >= 0xE000) {
+      lastPos = i + 1;
       out += hexTable[0xE0 | (c >> 12)] +
              hexTable[0x80 | ((c >> 6) & 0x3F)] +
              hexTable[0x80 | (c & 0x3F)];
       continue;
     }
     // Surrogate pair
     ++i;
-    c = 0x10000 + (((c & 0x3FF) << 10) | (str.charCodeAt(i) & 0x3FF));
+    var c2;
+    if (i < str.length)
+      c2 = str.charCodeAt(i) & 0x3FF;
+    else
+      c2 = 0;
+    lastPos = i + 1;
+    c = 0x10000 + (((c & 0x3FF) << 10) | c2);
     out += hexTable[0xF0 | (c >> 18)] +
            hexTable[0x80 | ((c >> 12) & 0x3F)] +
            hexTable[0x80 | ((c >> 6) & 0x3F)] +
            hexTable[0x80 | (c & 0x3F)];
   }
+  if (lastPos === 0)
+    return str;
+  if (lastPos < str.length)
+    return out + str.slice(lastPos);
   return out;
 };