Conclusion

Though themes differ from plugins and starters in many significant ways, they are useful for a variety of use cases, particularly to allow for packaged portions of functionality repeated across multiple sites to be managed gracefully as a single dependency. Though many Gatsby users will use Gatsby themes to override aesthetic elements to their heart’s content, others will override data queries or other functionality to more richly customize their sites with prefabricated code.

Gatsby themes also introduce two new concepts to our vocabulary: composition and shadowing. Theme composition is compelling because it allows us to combine arbitrary themes in a single Gatsby site. Meanwhile, theme shadowing is what allows us to override the files in individual themes to extend our sites with custom code.

Though themes are relatively new to the Gatsby ecosystem, they portend a new era of Gatsby development. And while this section concludes our examination of extending Gatsby, we will next turn to how to ensure Gatsby is ready for the real world through debugging and testing.