diff --git a/src/runtime/instance/api.js b/src/runtime/instance/api.js
deleted file mode 100644
index 20dea88c2..000000000
--- a/src/runtime/instance/api.js
+++ /dev/null
@@ -1,3 +0,0 @@
-export function apiMixin (Vue) {
-
-}
diff --git a/src/runtime/instance/events.js b/src/runtime/instance/events.js
index 24884112c..673e0fd5d 100644
--- a/src/runtime/instance/events.js
+++ b/src/runtime/instance/events.js
@@ -1,7 +1,86 @@
-export function initEvents (vm) {
+import { toArray } from '../util/index'
 
+export function initEvents (vm) {
+  vm._events = Object.create(null)
 }
 
 export function eventsMixin (Vue) {
+  Vue.prototype.$on = function (event, fn) {
+    (this._events[event] || (this._events[event] = []))
+      .push(fn)
+    return this
+  }
 
+  /**
+   * Adds an `event` listener that will be invoked a single
+   * time then automatically removed.
+   *
+   * @param {String} event
+   * @param {Function} fn
+   */
+
+  Vue.prototype.$once = function (event, fn) {
+    var self = this
+    function on () {
+      self.$off(event, on)
+      fn.apply(this, arguments)
+    }
+    on.fn = fn
+    this.$on(event, on)
+    return this
+  }
+
+  /**
+   * Remove the given callback for `event` or all
+   * registered callbacks.
+   *
+   * @param {String} event
+   * @param {Function} fn
+   */
+
+  Vue.prototype.$off = function (event, fn) {
+    var cbs
+    // all
+    if (!arguments.length) {
+      this._events = Object.create(null)
+      return this
+    }
+    // specific event
+    cbs = this._events[event]
+    if (!cbs) {
+      return this
+    }
+    if (arguments.length === 1) {
+      this._events[event] = null
+      return this
+    }
+    // specific handler
+    var cb
+    var i = cbs.length
+    while (i--) {
+      cb = cbs[i]
+      if (cb === fn || cb.fn === fn) {
+        cbs.splice(i, 1)
+        break
+      }
+    }
+    return this
+  }
+
+  /**
+   * Trigger an event on self.
+   *
+   * @param {String} event
+   */
+
+  Vue.prototype.$emit = function (event) {
+    var cbs = this._events[event]
+    if (cbs) {
+      cbs = cbs.length > 1 ? toArray(cbs) : cbs
+      var args = toArray(arguments, 1)
+      for (var i = 0, l = cbs.length; i < l; i++) {
+        cbs[i].apply(this, args)
+      }
+    }
+  }
 }
diff --git a/src/runtime/instance/index.js b/src/runtime/instance/index.js
index 6e5f7706c..133363fc2 100644
--- a/src/runtime/instance/index.js
+++ b/src/runtime/instance/index.js
@@ -1,7 +1,6 @@
 import { initState, stateMixin } from './state'
 import { initRender, renderMixin } from './render'
 import { initEvents, eventsMixin } from './events'
-import { apiMixin } from './api'
 
 export default function Vue (options) {
   this.$options = options
@@ -14,4 +13,3 @@ export default function Vue (options) {
 stateMixin(Vue)
 eventsMixin(Vue)
 renderMixin(Vue)
-apiMixin(Vue)
diff --git a/src/runtime/instance/state.js b/src/runtime/instance/state.js
index db246ce26..3aaca328e 100644
--- a/src/runtime/instance/state.js
+++ b/src/runtime/instance/state.js
@@ -83,35 +83,14 @@ function makeComputedGetter (getter, owner) {
 }
 
 function initMethods (vm) {
-  var methods = vm.$options.methods
+  const methods = vm.$options.methods
   if (methods) {
-    for (var key in methods) {
+    for (let key in methods) {
       vm[key] = bind(methods[key], vm)
     }
   }
 }
 
-function proxy (vm, key) {
-  if (!isReserved(key)) {
-    Object.defineProperty(vm, key, {
-      configurable: true,
-      enumerable: true,
-      get: function proxyGetter () {
-        return vm._data[key]
-      },
-      set: function proxySetter (val) {
-        vm._data[key] = val
-      }
-    })
-  }
-}
-
-function unproxy (vm, key) {
-  if (!isReserved(key)) {
-    delete vm[key]
-  }
-}
-
 export function stateMixin (Vue) {
   Object.defineProperty(Vue.prototype, '$data', {
     get () {
@@ -123,6 +102,18 @@ export function stateMixin (Vue) {
       }
     }
   })
+
+  Vue.prototype.$watch = function (fn, cb, options) {
+    options = options || {}
+    options.user = true
+    const watcher = new Watcher(this, fn, cb, options)
+    if (options.immediate) {
+      cb.call(this, watcher.value)
+    }
+    return function unwatchFn () {
+      watcher.teardown()
+    }
+  }
 }
 
 function setData (vm, newData) {
@@ -154,3 +145,24 @@ function setData (vm, newData) {
   observe(newData, vm)
   vm.$forceUpdate()
 }
+
+function proxy (vm, key) {
+  if (!isReserved(key)) {
+    Object.defineProperty(vm, key, {
+      configurable: true,
+      enumerable: true,
+      get: function proxyGetter () {
+        return vm._data[key]
+      },
+      set: function proxySetter (val) {
+        vm._data[key] = val
+      }
+    })
+  }
+}
+
+function unproxy (vm, key) {
+  if (!isReserved(key)) {
+    delete vm[key]
+  }
+}
diff --git a/src/runtime/observer/watcher.js b/src/runtime/observer/watcher.js
index 4357577b5..be04baa34 100644
--- a/src/runtime/observer/watcher.js
+++ b/src/runtime/observer/watcher.js
@@ -2,6 +2,7 @@ import config from '../config'
 import Dep from './dep'
 import { pushWatcher } from './batcher'
 import {
+  warn,
   extend,
   isArray,
   isObject,
@@ -51,7 +52,10 @@ export default function Watcher (vm, expOrFn, cb, options) {
   if (isFn) {
     this.getter = expOrFn
   } else {
-    this.getter = new Function(`with(this){return ${expOrFn}}`)
+    this.getter = function () {}
+    process.env.NODE_ENV !== 'production' && warn(
+      'Watcher only accpets function.'
+    )
   }
   this.value = this.lazy
     ? undefined