Clear History button will look disabled when there is no history

index.html

@@ -108,7 +108,7 @@
       <legend v-on:click="collapse">History ↕</legend>
       <div class="collapsible">
         <ul>
-          <li><button v-on:click="clearHistory">Clear History</button></li>
+          <li><button v-bind:class="{ disabled: noHistoryToClear }" v-on:click="clearHistory">Clear History</button></li>
         </ul>
         <ul v-for="entry in history">
           <li>

script.js

@@ -29,6 +29,11 @@ const app = new Vue({
     history: window.localStorage.getItem('history') ? JSON.parse(window.localStorage.getItem('history')) : []
   },
   computed: {
+
+    noHistoryToClear() {
+      return this.history.length === 0;
+    },
+
     urlNotValid() {
       const pattern = new RegExp('^(https?:\\/\\/)?' +
         '((([a-z\\d]([a-z\\d-]*[a-z\\d])*)\\.)+[a-z]{2,}|' +