fix: NavDropdown opens again

[maxbeier]

Problem

The dropdown menus (NavDropdown) in the header at https://primer.style/components/ currently don't seem to open.

Cause

It's kinda interesting: The details element registers an outside click handler on document to close if it's no longer needed. Unfortunately, React 17 changed the way its event delegation works, and does not listen on document anymore but the node it was mounted on.

So before upgrading the docs to use React 17, binding the click event was done when the event already reached document. But now, when the menu opens, the event bubbles up until it reaches document and triggers the newly added event listener which immediately closes the menu again. It therefore appears to never open.

Solution

This PR reverts the React version back to 16. It's only temporary until primer/doctocat#93 is merged, which replaces the current implementation of the dropdowns in the header navigation.

Screenshots

Merge checklist

• Added/updated tests
• Added/updated documentation
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge

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[smockle]

Thanks for the detailed write-up, @maxbeier! I appreciate your effort in tracking this down. Reviewing #942 (comment) makes me concerned about unforeseen consequences of rolling back the React version used on the docs site—I’ll follow-up on the status of primer/doctocat#93 before doing so.

[colebemis]

Fixed by #1340. Thanks again, @maxbeier!