Prevent SSR for amp-img occurring after second paragraph #1196
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| // the page performance even worse by eagerly loading an image outside the viewport. | ||
| if (!('data-hero' in node.attribs)) { | ||
| node.attribs['data-hero'] = ''; | ||
| imgNode.attribs['loading'] = 'lazy'; |
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I really like this approach. Have you checked if it is valid AMP?
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Yes, it is. The loading attribute is allowed, and it can be either lazy or eager: https://github.com/ampproject/amphtml/blob/a8889ac1b2622c461422a2186366f7a433848f44/validator/validator-main.protoascii#L3834-L3838
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Seems to be, otherwise the end-to-end spec would fail.
sebastianbenz
approved these changes
Apr 9, 2021
This was referenced Apr 9, 2021
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As pointed out by @jono-alderson, hero image prerendering can be detrimental when there are no hero images in the first viewport, as seen in these two examples from amp-wp.org:
This is especially problematic because
OptimizeHeroImagedoes not includeloading=lazyon the SSR'ed image. The result is that an optimized page may actually perform worse.This PR mitigates this issue by only doing hero image prerendering for images that appear before the second paragraph in the page.
Another mitigation measure is to add
loading=lazyto any SSR'ed hero image that was automatically detected. If a document haddata-heroon an image up front then theloading=lazywould remain omitted since the author is explicitly assuring the optimizer that the image should indeed be in the first viewport.