<span class="hljs-keyword">var</span> <span class="hljs-title function_">f</span> = x =&gt; x;
<span class="hljs-title function_">f</span>(<span class="hljs-function"><span class="hljs-params">x</span> =&gt;</span> x + <span class="hljs-function">(<span class="hljs-params">y=<span class="hljs-number">2</span>, z=<span class="hljs-literal">undefined</span>, ...rest</span>) =&gt;</span> y);
<span class="hljs-function">() =&gt;</span> <span class="hljs-literal">null</span>;
<span class="hljs-keyword">const</span> <span class="hljs-title function_">FC</span> = props =&gt; <span class="language-xml"><span class="hljs-tag">&lt;<span class="hljs-name">p</span>&gt;</span>functional component<span class="hljs-tag">&lt;/<span class="hljs-name">p</span>&gt;</span></span>;

<span class="hljs-keyword">const</span> <span class="hljs-title function_">good</span> = (<span class="hljs-params"></span>) =&gt; <span class="hljs-number">0</span>;
<span class="hljs-keyword">const</span> <span class="hljs-title function_">good</span> = (<span class="hljs-params">x</span>) =&gt; <span class="hljs-number">0</span>;
<span class="hljs-keyword">const</span> bad = (<span class="hljs-function"><span class="hljs-params">a</span> =&gt;</span> [...a, b]);
<span class="hljs-keyword">const</span> bad = (<span class="hljs-function"><span class="hljs-params">_</span> =&gt;</span> <span class="hljs-title function_">doSomething</span>());
<span class="hljs-keyword">const</span> bad = (<span class="hljs-function">() =&gt;</span> <span class="hljs-number">0</span>);
<span class="hljs-keyword">const</span> bad = (<span class="hljs-function">(<span class="hljs-params">a, b</span>) =&gt;</span> [...a, b]);
<span class="hljs-keyword">const</span> array = [<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>].<span class="hljs-title function_">reduce</span>(<span class="hljs-function">(<span class="hljs-params">acc, next</span>) =&gt;</span> [...acc, next], []);
sides.<span class="hljs-title function_">every</span>(<span class="hljs-function">(<span class="hljs-params">length,width=(<span class="hljs-number">3</span>+<span class="hljs-number">2</span>+(<span class="hljs-number">4</span>/<span class="hljs-number">5</span>))</span>) =&gt;</span> length &gt; <span class="hljs-number">0</span> );