title: JavaScript Calculate brighter colour
body: <p>I have a colour value in JS as a string</p>
  
  <pre><code>#ff0000
  </code></pre>
  
  <p>How would I go about programatically calculating a brighter/lighter version of this colour, for example <code>#ff4848</code>, and be able to calculate the brightness via a percentage, e.g.</p>
  
  <pre><code>increase_brightness('#ff0000', 50); // would make it 50% brighter
  </code></pre>