Bug#25465:
* lisp/progmodes/js.el (js-syntax-propertize): Recognize a regexp
literal after "!", "&", and "|".
test/lisp/progmodes/js-tests.el (js-mode-regexp-syntax): New test.
Bug#19399 and Bug#22431:
* lisp/progmodes/js.el (js-mode): Set comment-line-break-function and
c-block-comment-start-regexp.
* test/lisp/progmodes/js-tests.el: New file.