Vuejs get old value when on change event : <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>
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</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>
