Only show slot if it has content

It should be available at

this.$slots.footer

So, this should work.

hasFooterSlot() {
  return !!this.$slots.footer;
}

Example.

You should check vm.$slots and also vm.$scopedSlots for it.

hasSlot (name = 'default') {
   return !!this.$slots[ name ] || !!this.$scopedSlots[ name ];
}