opt: #17 promisify performance

src/promisify.js

@@ -1,27 +1,42 @@
 var _ = require("./_");
+var isFn = _.isFunction;
 
 module.exports = function (fn, self) {
-    return function () {
+    return function (a, b, c, d, e) {
         var len = arguments.length
-        , args = new Array(len);
+        , args, promise, resolve, reject;
 
-        for (var i = 0; i < len; i++) {
-            args[i] = arguments[i];
+        promise = new _.Promise(function (r, rj) {
+            resolve = r;
+            reject = rj;
+        });
+
+        function cb (err, val) {
+            err == null ? resolve(val) : reject(err);
         }
 
-        if (_.isFunction(args[len - 1])) {
-            return fn.apply(self, args);
+        switch (len) {
+        case 0: fn(cb); break;
+        case 1: isFn(a) ? fn(a) : fn(a, cb); break;
+        case 2: isFn(b) ? fn(a, b) : fn(a, b, cb); break;
+        case 3: isFn(c) ? fn(a, b, c) : fn(a, b, c, cb); break;
+        case 4: isFn(d) ? fn(a, b, c, d) : fn(a, b, c, d, cb); break;
+        case 5: isFn(e) ? fn(a, b, c, d, e) : fn(a, b, c, d, e, cb); break;
+        default:
+            args = new Array(len);
+
+            for (var i = 0; i < len; i++) {
+                args[i] = arguments[i];
+            }
+
+            if (isFn(args[len - 1])) {
+                return fn.apply(self, args);
+            }
+
+            args[i] = cb;
+            fn.apply(self, args);
         }
 
-        return new _.Promise(function (resolve, reject) {
-            args.push(function () {
-                if (arguments[0] != null) {
-                    return reject(arguments[0]);
-                } else {
-                    return resolve(arguments[1]);
-                }
-            });
-            return fn.apply(self, args);
-        });
+        return promise;
     };
 };

test/basic.js

@@ -236,6 +236,26 @@ module.exports = function (it) { return [
         return fn(0);
     }),
 
+    it("promisify promise 2", 3, function () {
+        var fn;
+        fn = utils.promisify(function (a, b, cb) {
+            return setTimeout(function () {
+                return cb(null, a + b);
+            });
+        });
+        return fn(1, 2);
+    }),
+
+    it("promisify promise err", "err", function () {
+        var fn;
+        fn = utils.promisify(function (a, cb) {
+            return setTimeout(function () {
+                return cb(a);
+            });
+        });
+        return fn("err").catch(function (v) { return v });
+    }),
+
     it("promisify callback", 1, function () {
         var fn;
         fn = utils.promisify(function (val, cb) {