title: Transform v-model bound value in Vue.js
body: <p>Consider this example:</p>
  
  <pre><code>&lt;input type="text" v-model="value"&gt;
  &lt;span&gt;Value is: {{ value }}&lt;/span&gt;
  </code></pre>
  
  <p>What I want is to put a bidirectional transformation function that would present the value in the input field in one form, but keep it in the data in another form. The simplest example would be negating numeric values: if the user inputs <code>5</code>, I'd like the data to actually receive <code>−5</code>. What would be the best way of accomplishing that in Vue.js 1.0?</p>