title: Update item field in Amazon DynamoDB without overwriting other fields
body: <p>I have an Amazon DynamoDB table called &quot;users' that has one user with the fields -UserId, FirstName, LastName, SignedInAt, SignedOutAt, IsSigned in.</p>
  <p>I want to only update certain fields, not all, but when I execute the following code, the fields that I am not updating disappear.</p>
  <p>So, I am just left with the UserID, SignedInAt, and IsSignedIn feilds. How do I update without the other fields disappearing?</p>
  <p>I am using JavaScript.</p>
  <p>Thanks!!!</p>
  <p>Before executing code:</p>
  <p><a href="https://i.stack.imgur.com/BcZBi.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/BcZBi.png" alt="enter image description here" /></a></p>
  <pre><code>await dynamo
        .put({
          TableName: &quot;users&quot;,
          Item: {
            UserId: requestJSON.UserId,
            SignedInAt: new Date().toLocaleTimeString(), // 11:18:48 AM
            IsSignedIn: true
          }
        })
        .promise();
  </code></pre>
  <p>After:</p>
  <p><a href="https://i.stack.imgur.com/QZTVi.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/QZTVi.png" alt="enter image description here" /></a></p>