util: Use of let and const. Optimized array use.

benchmark/arrays/push-vs-index-attribution.js

@@ -0,0 +1,51 @@
+'use strict';
+
+const common = require('../common.js');
+
+const obj = {
+  array_push______: function(n){
+    var arr = [];
+    for(let i=0; i<=n; i++) arr.push(i);
+
+    return arr;
+  },
+
+  array_unshift___: function(n){
+    var arr = [];
+    for(let i=n; i--;) arr.unshift(i);
+
+    return arr;
+  },
+
+  array_index_incr: function(n){
+    var arr = new Array(n);
+    for(let i=0; i<=n; i++) arr[i] = i;
+
+    return arr;
+  },
+
+  array_index_decr: function(n){
+    var arr = new Array(n);
+    for(let i=n; i--;) arr[i] = i;
+
+    return arr;
+  },
+};
+
+const bench = common.createBenchmark(main, {
+  type: Object.keys(obj),
+  n: [1000],
+});
+
+
+function main(conf) {
+  'use strict';
+  const
+    func = obj[conf.type],
+    n    = +conf.n;
+
+  bench.start();
+  func(n);
+  // console.log(String(func));
+  bench.end(n);
+}

lib/util.js

@@ -18,55 +18,35 @@ function tryStringify(arg) {
 }
 
 exports.format = function(f) {
+  const args = arguments;
+  const len  = args.length;
+
   if (typeof f !== 'string') {
-    const objects = new Array(arguments.length);
-    for (var index = 0; index < arguments.length; index++) {
-      objects[index] = inspect(arguments[index]);
+    const objects = new Array(len);
+    for (let i = len; i--;) {
+      objects[i] = inspect(args[i]);
     }
     return objects.join(' ');
   }
 
-  var argLen = arguments.length;
-
-  if (argLen === 1) return f;
-
-  var str = '';
-  var a = 1;
-  var lastPos = 0;
-  for (var i = 0; i < f.length;) {
-    if (f.charCodeAt(i) === 37/*'%'*/ && i + 1 < f.length) {
-      switch (f.charCodeAt(i + 1)) {
-        case 100: // 'd'
-          if (a >= argLen)
-            break;
-          if (lastPos < i)
-            str += f.slice(lastPos, i);
-          str += Number(arguments[a++]);
-          lastPos = i = i + 2;
-          continue;
-        case 106: // 'j'
-          if (a >= argLen)
-            break;
-          if (lastPos < i)
-            str += f.slice(lastPos, i);
-          str += tryStringify(arguments[a++]);
-          lastPos = i = i + 2;
-          continue;
-        case 115: // 's'
-          if (a >= argLen)
-            break;
-          if (lastPos < i)
-            str += f.slice(lastPos, i);
-          str += String(arguments[a++]);
-          lastPos = i = i + 2;
-          continue;
-        case 37: // '%'
-          if (lastPos < i)
-            str += f.slice(lastPos, i);
-          str += '%';
-          lastPos = i = i + 2;
-          continue;
-      }
+  if (len === 1) return f;
+
+  var i = 1;
+  var str = String(f).replace(formatRegExp, function(x) {
+    if (x === '%%') return '%';
+    if (i >= len) return x;
+    switch (x) {
+      case '%s': return String(args[i++]);
+      case '%d': return Number(args[i++]);
+      case '%j':
+        try {
+          return JSON.stringify(args[i++]);
+        } catch (_) {
+          return '[Circular]';
+        }
+        // falls through
+      default:
+        return x;
     }
     ++i;
   }