_.uniqWith() ↔ to return new duplicate-free Array with additional callback to control equality comparison

const tags = _.uniqWith(
    [
      ...alias_slugs,
      ...init_tags
        .concat(slug_key.replace(/-/g, " "))
        .filter((tag) => tag.length \> 0),
    ],
    (a, b) => a.toString().toLowerCase() === b.toString().toLowerCase()
  )

References