title: fill blank with elements of array
body: <p>I want to fill the '_' with reference array :</p>
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>const reference = ['this is', 'a beautiful', 'car'];
  const blank = ['I know', '_'];
  
  
  console.log(fillBlank(reference))
  
  function fillBlank(reference) {
  
      const ref = reference.join(' ');
  
      if(blank.length) {
      return // I know this is a beautiful car
    } else {
      return ref;
    }
    
  }</code></pre>
  </div>
  </div>
  </p>
  <p>Note that we may have blank in different places but we only have one in each blank array:</p>
  <pre><code>const blank = ['I know', '_'];
  const blank = ['_', 'I know'];
  const blank = ['I know', '_', 'right?'];
  </code></pre>
  <p>How can I do this?</p>