Sharing data between Office Add-Ins using localStorage

In this article I will show how the underlying dependence on the browser (in this case IE11 in Windows) allows us to pass data between Office Add-Ins through the use of HTML5 localStorage. At this point this is a theoretical post as I haven’t thought of a good use case yet, I am sure I will at some point…


Earlier this year I created a demo for the Salesforce global conference (Dreamforce) which showed how to create an Office Add-In to extract and manipulate Salesforce data from within an Office Add-In (you can see the presentation here). For the main demo I actually created one “Web Page” and reused it in the context of Word and Excel. In this article I will demonstrate how we can easily set a localStorage value in IE11 or in an Office Add-In and have that readable in the other client environments.


localStorage is part of the HTML5 Web Storage API which allows the permanent storage of string values in a browser. Like cookies the ability to read and write is tied to a domain. You can get/set values very easily by using the following notation:

  localStorage.setItem('name', 'Marky');
  localStorage.getItem('name'); //Marky

or even as simple as = 'Marky';; //Marky

The Embedded Browser 

When utilizing an Office Add-In within the Office client apps we are really using an embedded browser session within the context of the external client. In the case of Windows it is Internet Explorer. What this means though is that when we access a web domain, and set a localStorage value, that value is always available to us, when using Internet Explorer on that domain. Let me show you.

The Example

Here is my application running hosted on Azure in the domain


Through the console I created a new value

  localStorage.Marky = "This value set in IE11";

and as you can see below that is now accessible from localStorage


If I now load up my Office Add-In within Word we can see (using the F12 tool) that  it is the same URL (same web page). Because it is in the Add-In “host_Info=Word” is added to the URL but other than that it is the basically same.


Looking at the localStorage value we can also see “marky”


We can set a value here in Word


and then open the Add-In in Excel and retrieve the localStorage values previously set



If you have Word and Excel open you cannot set a localStorage value in one and have it picked up in the other, it seems that they only pick up the new values once they are opened. If you wanted to pass information between them in real time you could do that using WebSockets (something for a future demo).

Persistence between different Add-Ins

Now that I have set these values using the same application, we can also demonstrate that the principle is still applicable between different Add-Ins hosted in the same domain. In this example I have a different Add-In, still hosted on (this time in Outlook). All the localStorage values are still available to me.



In this article we have seen how we are able to set a localStorage value in Internet Explorer and then Word and have those values available in Excel. We have also seen that these values are actually available in other Add-Ins as long as they are hosted on the same domain.

This capability is all due to the underlying fact that Internet Explorer is the browser used to create all the demonstrated functionality.