title: update field with existing field in mongodb
body: <p>mongodb structure is like;</p>
  
  <pre><code>[
      {id: "1" , name: "alex"},
      {id: "2" , name: "felix"},
      {id: "3" , name: "kelix"},
      {id: "4" , name: "hannah"}
  ]
  </code></pre>
  
  <p>Let's assume I want to add "s" each document in the document.</p>
  
  <pre><code>[
      {id: "1" , name: "alexs"},
      {id: "2" , name: "felixs"},
      {id: "3" , name: "kelixs"},
      {id: "4" , name: "hannahs"}
  ]
  
  
  db.list.updateMany({}, { $set: {name: "$name" + "s"})}
  </code></pre>
  
  <p>But this followed by <code>script contains errors.</code></p>
  
  <p>Is it possible to update field with its existing value in mongodb?</p>