Web app preferred JPEG or PNG?

For watch web app, if we put in a few icons, which is faster for watch? JPEG or PNG?

Faster is PNG becuase lower encoding. But if you don’t need alpha channel you should use JPG to make final build smaller. Always try to save battery consuption and room on the watch’s storage due to UX rules.

Jpg is not always smaller. If your icons are rather geometrical shapes of one color tone than shaded images, the .png can give smaller and sharper result than .jpg Maybe better prepare both and decide after. In the example below, the images look same sharp, but jpg is 11kB and png only 2.7kB
testarrow testarrow
the third one is jpg with reduced quality to 20% in attempt to reduce size. Looks ugly, but its with 3.8kB still bigger than png so it has to be compared case to case.

Thanks. But if I can make the PNG similar to JPEG means PNG is preferred right (since it is faster)?

If you need simple icons like Peter shows you can use PNG even 8 bit. However, if you icons are very colourful I would use JPG format. You can check both version and take one better compressed.

In case decompression speed both PNG an JPG are good for you device and you rather don’t notice difference for small and a few icons.