title: How can I read Excel custom properties in Office Javascript API?
body: <p>I have a tab pane app that needs to access the custom properties of the current MS Office document, which can be Word or Excel.</p>
  
  <p>There seems to be no built in way of doing this with the Office JavaScript API, but in Word, I use the Office.context.document.getFileAsync() method to return the entire file. I can then unzip it, read in the custom.xml file, and navigate through the XML to get the custom properties. </p>
  
  <p>However, the Office.context.document.getFileAsync() is not available in Excel. Is there another way to read the custom properties?</p>