title: Get the difference of arrays in ES6?
body: <p>So I have two arrays:</p>
  
  <pre><code>const allLanguages = [ 'ES', 'EN', 'DE' ]
  const usedLanguages = [ { id: 1, lang: 'EN' } ]
  </code></pre>
  
  <p>What's the quickest way to produce a new array which is the difference between these two? In old school JavaScript, you'd have to do a for loop inside another for loop, I think...</p>
  
  <p>Eg:</p>
  
  <pre><code>const availableLanguages = [ 'ES', 'DE' ]
  </code></pre>