This is output after adding logging to AddMediaInfo pass just before these urls are added to the srcset attribute.
[subbu@earth:~/work/wmf/parsoid] echo "[[File:Foo.jpg|thumb]]" | php bin/parse.php --wt2html > /dev/null RESPONSIVE URLS: {"1.5":"https:\/\/upload.wikimedia.org\/wikipedia\/commons\/0\/06\/Foo.jpg","2":"https:\/\/upload.wikimedia.org\/wikipedia\/commons\/0\/06\/Foo.jpg"} [subbu@earth:~/work/wmf/parsoid] echo "[[File:Foo.jpg|thumb]]" | parse.js --useBatchAPI > /dev/null RESPONSIVE URLS: {"2":"https://upload.wikimedia.org/wikipedia/commons/0/06/Foo.jpg","1.5":"https://upload.wikimedia.org/wikipedia/commons/0/06/Foo.jpg"}
This causes spurious diffs when comparing output of PHP and JS runs.