how to get the changed value when change the form with vuejs form binding?
<h1>how to get the changed value when change the form with vuejs form binding?</h1>

<p>such as:</p>

<p>the data bind to form:</p>

<pre><code>{a:1, b:2, c:3}
</code></pre>

<p>after changed, it will be:</p>

<pre><code>{a:2, b:2, c:3}
</code></pre>

<p>and how to get the changed data:</p>

<pre><code>{a:2}
</code></pre>

<p>I mean that how to get the changed data such as the attrs a changed, then get the 
    {a:2}</p>