title: Outlook web add-in How to get customer properties via EWS in JS
body: <p>How to get customer properties via EWS in JS if I saved them via Outlook JS. API</p>
  <ol>
  <li><p>I saved custom properties using the following JS code:</p>
  <pre><code>   Office.context.mailbox.item.loadCustomPropertiesAsync(callback);
  
        function callback(asyncResult) {
        var customProps = asyncResult.value;
        customProps.set(&quot;isSync&quot;, &quot;test&quot;);
  
       // Save custom properties via JS API
       customProps.saveAsync(saveCallback);
      }
  </code></pre>
  </li>
  <li><p>Then I would like to get this custom prosperity via EWS.</p>
  </li>
  </ol>
  <p>Case 1:</p>
  <pre><code>   '&lt;t:ExtendedFieldURI PropertySetId=&quot;cecp-my manifest&quot; PropertyName=&quot;isSync&quot; PropertyType=&quot;String&quot;/&gt;' 
  </code></pre>
  <p>Case 2:</p>
  <pre><code>   '&lt;t:ExtendedFieldURI DistinguishedPropertySetId=&quot;PublicStrings&quot; PropertyName=&quot;isSync&quot; PropertyType=&quot;String&quot;/&gt;' 
  </code></pre>
  <p>Both approaches does not work. How should I describe &lt;t:AdditionalProperties&gt;?</p>
  <p>At the same time everything works if I use .Net:</p>
  <pre><code> ExtendedPropertyDefinition extendedPropertyDefinition = new ExtendedPropertyDefinition(DefaultExtendedPropertySet.PublicStrings, &quot;cecp-my manifest&quot;, MapiPropertyType.String);
   var props = new PropertySet(BasePropertySet.FirstClassProperties, ItemSchema.MimeContent, extendedPropertyDefinition);'
  </code></pre>