title: What does exclamation point after variable mean in JavaScript?
body: <p>I've seen in some React/TypeScript implementations such as : </p>
  
  <p><code>ref={ ref =&gt; this.container = ref! }</code></p>
  
  <p>What does the exclamation point means in <code>ref!</code>?
  Is that something specific in TypeScript, or a new standard JavaScript notation?</p>