Preloading static resources

Starting from version 9.0, you can preload static assets (HTML, CSS, JS, fonts) into the browser cache before opening a document to speed up the first-time loading of the document editor.

Two options are available.

Option 1. Using the ?preload=placeholder parameter

Append the ?preload=placeholder parameter to the api.js URL:

<div id="placeholder"></div>
<script type="text/javascript" src="https://documentserver/web-apps/apps/api/documents/api.js?preload=placeholder"></script>

Where documentserver is the name of the server with the ONLYOFFICE Docs installed.

In this case, in addition to creating DocsAPI.DocEditor, a hidden <iframe> will be automatically inserted into the DOM with id="placeholder", which loads static editor assets in the background.

Option 2. Manually inserting a preload iframe

Alternatively, you can insert a hidden <iframe> pointing to the preload page manually:

<iframe src="https://documentserver/web-apps/apps/api/documents/preload.html" style="display:none;"></iframe>

Where documentserver is the name of the server with the ONLYOFFICE Docs installed.

This option is recommended if you need to set additional security parameters for the iframe or use a nonce to insert into the DOM.

Use an <iframe> for preloading, not a <link rel="prefetch">. The editor's static assets (scripts, styles, fonts) are loaded within the iframe's context, and <link rel="prefetch"> will not correctly trigger their loading or caching.