title: Why do curly braces and/or whitespace make a difference?
body: <p>Why is this-</p>
  
  <pre><code>const squareList = (arr) =&gt; {
    "use strict";
    const sqr = arr.filter((numbers) =&gt; {
      numbers &gt; 0 &amp;&amp; Number.isInteger(numbers)
    }).map((numbers) =&gt; {
      Math.pow(numbers, 2)
      })
    return sqr;
  };
  </code></pre>
  
  <p>functionally different to this-</p>
  
  <pre><code>const squareddList = (arr) =&gt; { 
    "use strict";
    const sqr = arr.filter((numbers) =&gt; numbers &gt; 0 &amp;&amp; Number.isInteger(numbers)).map((numbers) =&gt; Math.pow(numbers, 2))
    return sqr; 
  }
  </code></pre>
  
  <p>when the only difference between them is whitespace and curly braces?</p>
  
  <p>When you pass an arbitrary array to both functions, the first returns an empty array and the second returns an array which has been filtered to only include positive integers and then squared.</p>