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On most pages iframe-resizer is able to detect changes in the iframe, recalculate the page size and adjust the iframe in sub nanosecond time. This page details the one of situation that can impact performance and how to mitigate it.

Content outside of the body element

By default iframe-resizer uses the size of the <body/> element to calculate the size of the iframe’s content. However, if it detects that their is content outside of the body, then iframe-resizer will fall back to checking the position of every visible element on the page.

In some cases, such as anchoring content to the base of the iframe, this can prevent the iframe from downsizing, as the content is now bound to the size of the window, rather than the content.

To address the issues raised by content overflow, you have two options.

  1. Adjust CSS and page design to keep all elements inside of the body element.

  2. Explicitly designate which page element should be used to track the page size, by adding a data-iframe-size attribute. This attribute can be added to multiple elements and the one that returns the highest value will be used each time the page size is calculated.

    This attribute should be used sparingly, as the more of them on the page, the greater the amount of work required to calculate the page size. It may also be useful to set the offset option as well.

If iframe-resizer detects content overflow is having an excessive impact on performance, it will log a warning to the browser console to advise you to add a data-iframe-size to an element on your page.

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