JSFiddle - React, Tailwind, and code Playground

HTML

<div id="mainapp">
      <span class="star" v-bind:class="{gold:obj.selected}" v-on:click="clickStar()">star</span>
    </div>

CSS

.star{
  color:#888;
}
.star.gold{
  color:#FFE957;
}

JavaScript

var app = new Vue({
      el:"#mainapp",
      data:{
        obj:{
        selected:false
        }  
      },
      methods:{
        clickStar:function(){
        if(this.obj.selected == false){
        	this.obj.selected = true;
        }
        }
      }
    })