Diff JavaScript (or any other type of file) across two production branches

diffbranches

#!/usr/bin/env bash
file_pattern='*.js'      # Which files to consider
v1="php-1.28.0-wmf.18"   # Base branch
v2="php-1.28.0-wmf.17"   # Target branch
while IFS= read -r a; do
  b="${a/$v1/$v2}"
  diff -u "$a" "$b"      # Change '-u' to '-q' if you only want
                         # to list which files have changed.
done < <(find "/srv/mediawiki/${v1}" -name "$file_pattern")