Web components SEO

Testing indexability of web components.

This website tests how standard and custom HTML tags are indexed by Google under different circumstances.

Standard HTML

Content	Javascript	Link	Seen by Google
async javascript	ES5	/html-dynamic-async	no

Custom HTML

Content	Tag definition	Shadow DOM	Javascript	Link	Seen by Google
sync javascript	immediate	no	ES5	/noshadow-dynamic-sync-es5	no
sync javascript	immediate	no	ES6	/noshadow-dynamic-sync	no
sync javascript	immediate	yes	ES5	/shadow-dynamic-sync-es5	no
sync javascript	immediate	yes	ES6	/shadow-dynamic-sync	no
async javascript	lazy	no	ES6	/noshadow-dynamic-async	no
async javascript	lazy	yes	ES6	/shadow-dynamic-async	no

Conclusion

Google can always see static HTML content on the page, in standard or custom HTML tags.

When it comes to Javascript-rendered content, Google completely ignores custom HTML tags but not standard ones.