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. You can register a free ONLYOFFICE Cloud and use its public IP address or public DNS that can be found in the Instances section of the cloud console.

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. You can register a free ONLYOFFICE Cloud and use its public IP address or public DNS that can be found in the Instances section of the cloud console.

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.