It looks wrong to require from users to add mappings for both `js-mode'
and its alias `javascript-mode' to `major-mode-remap-alist':

  (add-to-list 'major-mode-remap-alist '(js-mode . js-ts-mode))
  (add-to-list 'major-mode-remap-alist '(javascript-mode . js-ts-mode))

Either `major-mode-remap-alist' could support aliases, or simpler
would be just to replace the alias in `auto-mode-alist':