Good question - the code tries to fetch the images ahead of them coming into the viewport. That can mean upon section expansion, as well.

On Tuesday, August 23, 2016, Justin Ormont <> wrote:
This sounds great. Are the images pre-loaded when the user gets close, or once it's scrolled into view?


On Tue, Aug 23, 2016 at 3:48 PM, Volker Eckl <> wrote:
Amazing work! Enjoying the further speed improvements and the detailed analysis of Japanese Wikipedia testcase.

On Tue, Aug 23, 2016 at 2:20 PM, Jon Robson <> wrote:
FYI after much experimentation, research and testing the mobile site has been lazy loading images [1] since Thursday 18th August. This means if you do not see an image you will not download it. We have taken care to ensure users without JavaScript can still view images and that most users will barely notice the difference.

We are currently crunching the data this change has made and we plan to write a blog post to reporting the results.

In our experiments on Japanese Wikipedia we saw a drop in image bytes per page view by 54% On the Japanese Japan article bytes shipped to users dropped from 1.443 MB to 142 kB.

This is pretty huge since bytes equate to money [3] and we expect this to be significant on wikis where mobile data is more expensive. In a nutshell Wikipedia mobile is cheaper.

As I said blog post to follow once we have more information, but please report any bugs you are seeing with the implementation (we have already found a few thanks to our community of editors).


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