title: Vuejs get old value when on change event
body: <p>Please refer to my snippet below. How can I get the old value of the changed model, in this case is the age in vuejs?</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>var app = new Vue({
    el:"#table1",
    data:{
     items:[{name:'long name One',age:21},{name:'long name Two',age:22}]
    },
    methods:{
      changeAge:function(item,event){
        alert(item.age);
      }
    }
  });</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"&gt;&lt;/script&gt;
  &lt;script src="https://unpkg.com/vue/dist/vue.js"&gt;&lt;/script&gt;
  
  &lt;table class="table table-cart" id="table1"&gt;
     &lt;thead&gt;
       &lt;tr&gt;
         &lt;th&gt;Name&lt;/th&gt;
         &lt;th&gt;Age&lt;/th&gt;
       &lt;/tr&gt;
    &lt;/thead&gt;
     &lt;tbody&gt;
       &lt;tr v-for="(item,index) in items"&gt;
         &lt;td&gt;{{item.name}} :&lt;/td&gt;       
         &lt;td&gt;
           &lt;input type="text" name="qty"
                  v-model="item.age"   
                  @change="changeAge(item,$event)"&gt;
         &lt;/td&gt;
       &lt;/tr&gt;
     &lt;/tbody&gt;
   &lt;/table&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>I am trying to use watch, but I am not able to find any help in watching the age an array of items.  </p>