Resizing does not work when the host page uses jQuery and iframeResizer.js included to the host page repeatedly

[dshiryaev-plesk]

Version

3.5.5

Precondition

• the host page has jQuery loaded
• the host page have two iframes with content that changes its height dynamically
• every of the iframes do the following:
  • includes iframeResizer.contentWindow.js
  • adds script iframeResizer.js to the host page
  • adds the following call to initialize itself to a script in the host page's body: jQuery('#' + window.frameElement.id).iFrameResize()

Steps to reproduce

• open host page
• change the height of content of any iframe

Expected result

The height of the iframe has changed

Actual result

• The height of the iframe is NOT has changed
• browser's console has messages like the following:
  Sending message to host page (iframe-43993:1921:568:mutationObserver)
  Ignored: iframe-43993:1921:568:mutationObserver

Help to fix

iframeResizer.js: 982

[davidjbradshaw]

If you want to create a patch that checks if the jQuery plugin is already loaded, before adding it. Then happy to take the PR.