title: What is really the difference between underscore _.each and _.map?
body: <p>I'm using UnderscoreJs. Consider this code: </p>
  
  <pre><code>var docs = [
      {name : 'Anders', niche : 'Web Development'}, 
      {name : 'Johnny', niche : 'Design'}, 
      {name : 'Eric', niche : 'PhotoShop'}
  ];
  
  var newDocs = _.map(docs, function (doc){
      delete doc.niche;
      return doc;
  });
  </code></pre>
  
  <p>It doesn't matter if I use <code>.each</code> or <code>.map</code> here. The outcome is exactly the same. </p>
  
  <p>What is really the difference between the two in the case above?</p>