fix utils.warn not stripped in prod build

Author: Evan You

src/directive.js

@@ -191,7 +191,10 @@ Directive.split = function (exp) {
 Directive.parse = function (dirname, expression, compiler, node) {
 
     var dir = compiler.getOption('directives', dirname) || directives[dirname]
-    if (!dir) return utils.warn('unknown directive: ' + dirname)
+    if (!dir) {
+        utils.warn('unknown directive: ' + dirname)
+        return
+    }
 
     var rawKey
     if (expression.indexOf('|') > -1) {
@@ -204,9 +207,11 @@ Directive.parse = function (dirname, expression, compiler, node) {
     }
 
     // have a valid raw key, or be an empty directive
-    return (rawKey || expression === '')
-        ? new Directive(dirname, dir, expression, rawKey, compiler, node)
-        : utils.warn('invalid directive expression: ' + expression)
+    if (rawKey || expression === '') {
+        return new Directive(dirname, dir, expression, rawKey, compiler, node)
+    } else {
+        utils.warn('invalid directive expression: ' + expression)
+    }
 }
 
 module.exports = Directive

src/directives/on.js

@@ -1,4 +1,5 @@
-var warn = require('../utils').warn
+var utils    = require('../utils'),
+    noBubble = ['blur', 'focus', 'load']
 
 module.exports = {
 
@@ -7,15 +8,16 @@ module.exports = {
     bind: function () {
         // blur and focus events do not bubble
         // so they can't be delegated
-        this.bubbles = this.arg !== 'blur' && this.arg !== 'focus'
+        this.bubbles = noBubble.indexOf(this.arg) === -1
         if (this.bubbles) {
             this.binding.compiler.addListener(this)
         }
     },
 
     update: function (handler) {
         if (typeof handler !== 'function') {
-            return warn('Directive "on" expects a function value.')
+            utils.warn('Directive "on" expects a function value.')
+            return
         }
         var targetVM = this.vm,
             ownerVM  = this.binding.compiler.vm,

src/directives/partial.js

@@ -13,8 +13,10 @@ module.exports = {
         var partial = id === 'yield'
             ? this.compiler.rawContent
             : this.compiler.getOption('partials', id)
+
         if (!partial) {
-            return utils.warn('Unknown partial: ' + id)
+            utils.warn('Unknown partial: ' + id)
+            return
         }
 
         // comment ref node means inline partial

src/main.js

@@ -63,7 +63,8 @@ ViewModel.use = function (plugin) {
         try {
             plugin = require(plugin)
         } catch (e) {
-            return utils.warn('Cannot find plugin: ' + plugin)
+            utils.warn('Cannot find plugin: ' + plugin)
+            return
         }
     }