Vue

HTML

<div id="app">
  <h2>Todos:</h2>
  <ol>
    <li v-for="(todo, idx) in todos">
      <label>
        <a href="#"
          v-on:click="toggle(idx)"
          v-bind:checked="todo.done"
          :class="{'active': idx == activeIndex}"
          >
          {{ todo.text }}
       
        </a>

      </label>
    </li>
  </ol>
</div>

CSS

body {
  background: #20262E;
  padding: 20px;
  font-family: Helvetica;
}

#app {
  background: #fff;
  border-radius: 4px;
  padding: 20px;
  transition: all 0.2s;
}

li {
  margin: 8px 0;
}

h2 {
  font-weight: bold;
  margin-bottom: 15px;
}

del {
  color: rgba(0, 0, 0, 0.3);
}

.active {
  color: red;
}

Vue

new Vue({
  el: "#app",
  data: {
  	activeColor:String,
    todos: [
      { text: "Learn JavaScript", done: false },
      { text: "Learn Vue", done: false },
      { text: "Play around in JSFiddle", done: false },
      { text: "Build something awesome", done: false }
    ],
    activeIndex: null
  },
  methods: {
  	toggle: function(index){
    	this.activeIndex = index
    }
  }
})