title: Declaring 2 undefined variables in a variable then using it
body: <p>I've recently saw this code in a discord server:</p>
  <pre class="lang-js prettyprint-override"><code>const image = Image.new(1024, 1024)
  const a = 32
  let g = (b, c) =&gt; b+a * c+a // what's the math behind this? b and c is undefined.
  image.fill(g)
  </code></pre>
  <p>(image is an image manipulation module)</p>
  <p>My question is, how the variable <code>g</code> works when it generates the image? Image.fill() goes through the each pixel of the image and set a color, but I don't understand the math behind <code>let g = (b, c) =&gt; b+a * c+a</code></p>