optimize loops

src/binding.js

@@ -35,7 +35,7 @@ p._addChild = function (key, child) {
  */
 
 p._addSub = function (sub) {
-  this._subs.push(sub)
+  this._subs.unshift(sub)
 }
 
 /**
@@ -53,7 +53,8 @@ p._removeSub = function (sub) {
  */
 
 p._notify = function () {
-  for (var i = 0, l = this._subs.length; i < l; i++) {
+  var i = this._subs.length
+  while (i--) {
     this._subs[i].update()
   }
 }

src/emitter.js

@@ -9,7 +9,7 @@ var _ = require('./util')
 
 function Emitter (ctx) {
   this._cancelled = false
-  this._ctx = ctx || this
+  this._ctx = ctx || null
 }
 
 var p = Emitter.prototype
@@ -25,7 +25,7 @@ var p = Emitter.prototype
 p.on = function (event, fn) {
   this._cbs = this._cbs || {}
   ;(this._cbs[event] || (this._cbs[event] = []))
-    .push(fn)
+    .unshift(fn)
   return this
 }
 
@@ -76,7 +76,8 @@ p.off = function (event, fn) {
   }
   // remove specific handler
   var cb
-  for (var i = 0; i < callbacks.length; i++) {
+  var i = callbacks.length
+  while (i--) {
     cb = callbacks[i]
     if (cb === fn || cb.fn === fn) {
       callbacks.splice(i, 1)
@@ -99,8 +100,10 @@ p.emit = function (event, a, b, c, d) {
   var callbacks = this._cbs[event]
   if (callbacks) {
     callbacks = _.toArray(callbacks)
-    for (var i = 0, l = callbacks.length; i < l; i++) {
-      callbacks[i].call(this._ctx, a, b, c, d)
+    var i = callbacks.length
+    var ctx = this._ctx
+    while (i--) {
+      callbacks[i].call(ctx, a, b, c, d)
     }
   }
   return this
@@ -121,14 +124,14 @@ p.applyEmit = function (event) {
   if (callbacks) {
     // avoid leaking arguments:
     // http://jsperf.com/closure-with-arguments
-    var i
-    var l = arguments.length
-    var args = new Array(l - 1)
-    for (i = 1; i < l; i++) {
-      args[i - 1] = arguments[i]
+    var i = arguments.length - 1
+    var args = new Array(i)
+    while (i--) {
+      args[i] = arguments[i + 1]
     }
     callbacks = _.toArray(callbacks)
-    for (i = 0, l = callbacks.length; i < l; i++) {
+    i = callbacks.length
+    while (i--) {
       if (callbacks[i].apply(this._ctx, args) === false) {
         this._cancelled = true
       }

src/filters/array-filters.js

@@ -22,14 +22,15 @@ exports._objToArray = function (obj) {
     )
     return
   }
-  var res = []
   var keys = Object.keys(obj)
-  for (var i = 0, l = keys.length, key; i < l; i++) {
+  var i = keys.length
+  var res = new Array(i)
+  while (i--) {
     key = keys[i]
-    res.push({
+    res[i] = {
       key: key,
       value: obj[key]
-    })
+    }
   }
   res._converted = true
   return res

src/instance/compile.js

@@ -210,7 +210,7 @@ exports._checkPriorityDirs = function (node) {
   }
   var value, dir
   /* jshint boss: true */
-  for (var i = 0, l = priorityDirs.length; i < l; i++) {
+  for (var i = 0; i < 3; i++) {
     dir = priorityDirs[i]
     if (value = _.attr(node, dir)) {
       this._bindDirective(dir, value, node)

src/observe/array-augmentations.js

@@ -21,9 +21,9 @@ var arrayAugmentations = Object.create(Array.prototype)
   function mutator () {
     // avoid leaking arguments:
     // http://jsperf.com/closure-with-arguments
-    var l = arguments.length
-    var args = new Array(l)
-    for (var i = 0; i < l; i++) {
+    var i = arguments.length
+    var args = new Array(i)
+    while (i--) {
       args[i] = arguments[i]
     }
     var result = original.apply(this, args)

src/observe/observer.js

@@ -132,7 +132,8 @@ p.walk = function (obj) {
 
 p.link = function (items, index) {
   index = index || 0
-  for (var i = 0, l = items.length; i < l; i++) {
+  var i = items.length
+  while (i--) {
     this.observe(i + index, items[i])
   }
 }
@@ -144,7 +145,8 @@ p.link = function (items, index) {
  */
 
 p.unlink = function (items) {
-  for (var i = 0, l = items.length; i < l; i++) {
+  var i = items.length
+  while (i--) {
     this.unobserve(items[i])
   }
 }
@@ -192,7 +194,8 @@ p.unobserve = function (val) {
   if (val && val.$observer) {
     val.$observer.parentsHash[this.id] = null
     var parents = val.$observer.parents
-    for (var i = 0, l = parents.length; i < l; i++) {
+    var i = parents.length
+    while (i--) {
       if (parents[i].ob === this) {
         parents.splice(i, 1)
         break
@@ -243,9 +246,12 @@ p.convert = function (key, val) {
 p.propagate = function (event, path, val, mutation) {
   this.emit(event, path, val, mutation)
   var parents = this.parents
+  if (!parents) {
+    return
+  }
   var parent, key, parentPath
-  if (!parents) return
-  for (var i = 0, l = parents.length; i < l; i++) {
+  var i = parents.length
+  while (i--) {
     parent = parents[i]
     key = parent.key
     parentPath = path

src/util/lang.js

@@ -69,10 +69,10 @@ exports.bind = function (fn, ctx) {
 
 exports.toArray = function (list, start) {
   start = start || 0
-  var l = list.length
-  var ret = new Array(l - start)
-  for (var i = start; i < l; i++) {
-    ret[i - start] = list[i]
+  var i = list.length - start
+  var ret = new Array(i)
+  while (i--) {
+    ret[i] = list[i + start]
   }
   return ret
 }