title: Vuelidate how to conditionally disable submit button
body: <p>How can I conditionally disable the submit button of my Vuelidate form if all the fields don't meet the required criteria?</p>
  
  <p>I tried the below but <code>:disabled</code> will only accept the word disabled in there.</p>
  
  <pre class="lang-html prettyprint-override"><code>&lt;form&gt;
    &lt;ol&gt;
      &lt;li class="inputQuestion" v-bind:class="{ 'error': $v.user.username.$error }"&gt;
        &lt;label&gt;Username:&lt;/label&gt;
        &lt;input v-model.trim="user.username" @input="$v.user.username.$touch()" /&gt;
      &lt;/li&gt;
      &lt;li class="inputQuestion" v-bind:class="{ 'error': $v.user.password.$error }"&gt;
        &lt;label&gt;Password:&lt;/label&gt;
        &lt;input v-model.trim="user.password" @input="$v.user.password.$touch()" /&gt;
      &lt;/li&gt;
  
      &lt;li class="submission"&gt;
        &lt;button @click.prevent="submitForm" :disabled="$v.form.valid()"&gt;Sign In&lt;/button&gt;
      &lt;/li&gt;
    &lt;/ol&gt;
  &lt;/form&gt;
  </code></pre>