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Build nested comments

MediumP2Build

Build a nested comments component in React where users can reply at any depth, edit, delete, vote and collapse threads.

Time box: 60 to 75 minutes.

Requirements

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Renders a tree of comments from initial data, with indentation or a left guide line for depth
A Reply button opens an inline form under that comment; submitting adds a child at any depth
Edit and Delete work on the author's own comments; deleting a comment with replies keeps the thread (shows "[deleted]") instead of removing the children
Each comment can be collapsed and expanded, hiding its descendants and showing a count of hidden replies
Upvote and downvote with one vote per user per comment, toggling and switching, and a visible score
State is normalised (a map of comments by id plus a children or parentId field), not a deeply nested object that must be cloned to update

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