<p dir="auto"><a href="https://babeljs.io/repl/#?experimental=true&amp;evaluate=true&amp;loose=false&amp;spec=false&amp;playground=false&amp;code=%40test(()%20%3D%3E%20123)%0Aclass%20A%20%7B%7D%0A%0A%40test(()%20%3D%3E%20%7B%20return%20123%20%7D)%0Aclass%20B%20%7B%7D%0A%0A%40test(function()%20%7B%20return%20123%20%7D)%0Aclass%20%D0%A1%20%7B%7D" rel="nofollow">https://babeljs.io/repl/#?experimental=true&amp;evaluate=true&amp;loose=false&amp;spec=false&amp;playground=false&amp;code=%40test(()%20%3D%3E%20123)%0Aclass%20A%20%7B%7D%0A%0A%40test(()%20%3D%3E%20%7B%20return%20123%20%7D)%0Aclass%20B%20%7B%7D%0A%0A%40test(function()%20%7B%20return%20123%20%7D)%0Aclass%20%D0%A1%20%7B%7D</a></p>
<p dir="auto">Compare the output of these two to show the difference.</p>
<p dir="auto"><a href="https://babeljs.io/repl/#?experimental=true&amp;evaluate=true&amp;loose=false&amp;spec=false&amp;code=%40decorate((arg)%20%3D%3E%20null)%0Aclass%20Example1%20%7B%0A%7D%0A%0A%40decorate(arg%20%3D%3E%20null)%0Aclass%20Example2%20%7B%0A%7D" rel="nofollow">https://babeljs.io/repl/#?experimental=true&amp;evaluate=true&amp;loose=false&amp;spec=false&amp;code=%40decorate((arg)%20%3D%3E%20null)%0Aclass%20Example1%20%7B%0A%7D%0A%0A%40decorate(arg%20%3D%3E%20null)%0Aclass%20Example2%20%7B%0A%7D</a></p>
<div class="highlight highlight-source-js notranslate position-relative overflow-auto" dir="auto" data-snippet-clipboard-copy-content="@decorate((arg) =&gt; null)
class Example1 {
}

@decorate(arg =&gt; null)
class Example2 {
}"><pre class="notranslate">@<span class="pl-en">decorate</span><span class="pl-kos">(</span><span class="pl-kos">(</span><span class="pl-s1">arg</span><span class="pl-kos">)</span> <span class="pl-c1">=&gt;</span> <span class="pl-c1">null</span><span class="pl-kos">)</span>
<span class="pl-k">class</span> <span class="pl-v">Example1</span> <span class="pl-kos">{</span>
<span class="pl-kos">}</span>

@<span class="pl-en">decorate</span><span class="pl-kos">(</span><span class="pl-s1">arg</span> <span class="pl-c1">=&gt;</span> <span class="pl-c1">null</span><span class="pl-kos">)</span>
<span class="pl-k">class</span> <span class="pl-v">Example2</span> <span class="pl-kos">{</span>
<span class="pl-kos">}</span></pre></div>