title: What's a unique key in vue.js used for?
body: <p>What I mean is this:</p>
  
  <p>Let's say we have a v-for directive in our custom vue component used in the following way:</p>
  
  <p><code>&lt;my-custom-component v-for="item in items" :key="item.id"&gt;{{item.remark}}&lt;/ my-custom-component&gt;</code></p>
  
  <p>What is the purpose of using <code>:key="item.id"</code> here?</p>