title: Email validation n vuetify.js
body: <p>I have an email field </p>
  
  <pre><code>    &lt;template&gt;
    &lt;v-form v-model="valid"&gt;
      &lt;v-text-field
        label="Name"
        v-model="name"
        :rules="nameRules"
        :counter="10"
        required
      &gt;&lt;/v-text-field&gt;
      &lt;v-text-field
        label="E-mail"
        v-model="email"
        :rules="emailRules"
  
      &gt;&lt;/v-text-field&gt;
    &lt;/v-form&gt;
  &lt;/template&gt;
  </code></pre>
  
  <p>and validation rule like, </p>
  
  <pre><code> &lt;script&gt;
    export default {
      data: () =&gt; ({
        valid: false,
        name: '',
        nameRules: [
          v =&gt; !!v || 'Name is required',
          v =&gt; v.length &lt;= 10 || 'Name must be less than 10 characters'
        ],
        email: '',
        emailRules: [ 
          v =&gt; /^\w+([.-]?\w+)*@\w+([.-]?\w+)*(\.\w{2,3})+$/.test(v) || 'E-mail must be valid'
        ]
      })
    }
  &lt;/script&gt;
  </code></pre>
  
  <p>but it validate form whnever i submit the form, i need to validate email only when email.length>0 . ie email is not a required field, but if email typed , it must be validate.</p>
  
  <p>also tried,
  when i change <code>:rules="[emailRules.em]"</code>  like this and in script</p>
  
  <pre><code>emailRules: { 
                          em:v =&gt; {
                          if(v.length &gt; 0 &amp;&amp; /^\w+([.-]?\w+)*@\w+([.-]?\w+)*(\.\w{2,3})+$/.test(v) )
                              return ''E-mail must be valid';  
                            return true;
                      }
                      }
  </code></pre>
  
  <p>it always return true</p>