[GitHub] [incubator-pagespeed-ngx] Lofesa edited a comment on issue #1663: Chrome's Native Lazy Loading

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Lofesa edited a comment on issue #1663: Chrome's Native Lazy Loading
URL: https://github.com/apache/incubator-pagespeed-ngx/issues/1663#issuecomment-531503659
 
 
   Hi @jmarantz 
   No, the beacon to "see" if the image is or not above the fold is not needed when the browser can do the lazyload work. As far as I know this, is the browser who decides when the image is loaded. The loading attribute mus be set allways, then if the browser is capable to do the lazyload it decides what images to load and when.
   So we need to set `loading=lazy` allways, if not present, and test if the browser is capable or not, if not, we need to do all the work for lazyload the image.
   Is a similar thing as if the image has data-src, if the image has it we do nothing to lazyload the image as far as we know other lazyload software is present.
   We can test the browser capability by 2 ways, have a whitelist of UA ( at the moment only chrome version > 76 ) or asking to the browser.
   The 1st way need to do a maintenance of the whitelist, adding versions and browser that support this feature.
   The 2snd, way is making a big if in the javascript snipet, if browser is capable or if not.
   Some like:
   ```
   if ('loading' in HTMLImageElement.prototype) {
     // supported in browser
   } else {
     // fetch polyfill/third-party library
   }
   ```
   If supported in browser we need to copy data-src and data-srcset to src and srcset in all images. If not we need to do all the work that the actual javascript snipet do.
   
   
   Hope all this is well expressed.

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