diff --git a/src/compiler/codegen.js b/src/compiler/codegen.js
index 501ce0aa..48294e4c 100644
--- a/src/compiler/codegen.js
+++ b/src/compiler/codegen.js
@@ -86,7 +86,7 @@ function genChildren (el) {
   if (!el.children.length) {
     return 'undefined'
   }
-  return '__flatten__([' + el.children.map(genNode).join(',') + '])'
+  return '[' + el.children.map(genNode).join(',') + ']'
 }
 
 function genNode (node) {
diff --git a/src/instance/index.js b/src/instance/index.js
index 8f7028df..e4643c22 100644
--- a/src/instance/index.js
+++ b/src/instance/index.js
@@ -43,23 +43,6 @@ export default class Component {
       : dynamic
   }
 
-  __flatten__ (arr) {
-    var res = []
-    for (var i = 0, l = arr.length; i < l; i++) {
-      var e = arr[i]
-      if (Array.isArray(e)) {
-        for (var j = 0, k = e.length; j < k; j++) {
-          if (e[j]) {
-            res.push(e[j])
-          }
-        }
-      } else if (e) {
-        res.push(e)
-      }
-    }
-    return res
-  }
-
   _proxy (key) {
     if (!isReserved(key)) {
       // need to store ref to self here
diff --git a/src/vdom/h.js b/src/vdom/h.js
index 15af6e46..369d7e59 100644
--- a/src/vdom/h.js
+++ b/src/vdom/h.js
@@ -10,24 +10,29 @@ function addNS(data, children) {
   }
 }
 
-export default function h (tag, b, c) {
-  var data = {}, children, text, i
-  if (arguments.length === 3) {
-    data = b
-    if (isArray(c)) { children = c }
-    else if (isPrimitive(c)) { text = c }
-  } else if (arguments.length === 2) {
-    if (isArray(b)) { children = b }
-    else if (isPrimitive(b)) { text = b }
-    else { data = b }
-  }
+export default function h (tag, data, children) {
   if (isArray(children)) {
-    for (i = 0; i < children.length; ++i) {
-      if (isPrimitive(children[i])) children[i] = VNode(undefined, undefined, undefined, children[i])
+    let _children = children
+    children = []
+    for (let i = 0, l = _children.length; i < l; i++) {
+      let e = _children[i]
+      // flatten nested
+      if (isArray(e)) {
+        for (let j = 0, k = e.length; j < k; j++) {
+          if (e[j]) {
+            children.push(e[j])
+          }
+        }
+      } else if (isPrimitive(e)) {
+        // convert primitive to vnode
+        children.push(VNode(undefined, undefined, undefined, e))
+      } else if (e) {
+        children.push(e)
+      }
     }
   }
   if (tag === 'svg') {
     addNS(data, children)
   }
-  return VNode(tag, data, children, text, undefined)
+  return VNode(tag, data, children, undefined, undefined)
 }
diff --git a/src/vdom/vnode.js b/src/vdom/vnode.js
index 628bf873..ba7c9cca 100644
--- a/src/vdom/vnode.js
+++ b/src/vdom/vnode.js
@@ -1,4 +1,3 @@
 export default function VNode (sel, data, children, text, elm) {
-  const key = data === undefined ? undefined : data.key
-  return { sel, data, children, text, elm, key }
+  return { sel, data, children, text, elm, key: data && data.key }
 }