title: Promise.all with nested Promise.all
body: <p>I've nested arrays, I'm able to retrieve promises for the 2nd level array but not sure how to implement a <code>then</code> once top level finishes as well.</p>
  
  <pre><code>result.forEach(function(entity){ // outer list ???
      return Promise.all(entity.urls.map(function(item){
          return requestURL(item.href);
      }));
  });
  </code></pre>
  
  <p>for instance if <code>results</code> has two or more items and each <code>item</code> has 10 or more urls to fetch, how would we implement <code>then</code> of <code>[Promise.all][1]</code> for all the promises. Native solution please.</p>
  
  <p>Basically to handle nested arrays of promises in a right way.</p>
  
  <p><strong>Data Structure:</strong></p>
  
  <pre><code>var result = [
      {
          urls: [
              {href: "link1"},
              {href: "link2"},
              {href: "link3"}
          ]
      },
      {
          urls: [
              {href: "link4"},
              {href: "link5"},
              {href: "link6"}
          ]
      }
  ];
  </code></pre>