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Preloading static content

One way to improve the load time performance of Office Online applications is to preload Office Online's static content (JavaScript, CSS, and images) into the user's browser cache. This will help ensure that when the user opens a document in Office Online, they can use the previously cached static content and do not need to download that data when they first try to load Office Online.

To support preloading static content, Office Online provides two WOPI actions for each Office Online application in its discovery XML, one to preload static content for the :wopi:action:`view` action (:wopi:action:`preloadview`), and a second to preload static content for the :wopi:action:`edit` action (:wopi:action:`preloadedit`).

Hosts can use these URLs just like they use other :ref:`Action URLs`, by pointing iframes in their pages at the action URL. Unlike most action URLs, the WopiSrc and access token do not need to be specified in order to use these actions.

Hosts can include both :wopi:action:`preloadview` and :wopi:action:`preloadedit` in their pages to preload static content for both. Note that the static content preload actions contain the :term:`UI_LLCC` placeholder value, which should be replaced with an appropriate language for the user so that the proper localized static content is preloaded.


If you wish to preload static content for all applications and both view and edit modes, you must load multiple actions, one for each application/mode combination.

|stub-icon| Optimizing document viewing for high volume

issue:: 5
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