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Nested Comments (Infinite Replies)

By FrontendAtlas Team · Updated Jan 30, 2026

Build a nested comments panel that supports infinite-depth replies. Users can add top-level comments and reply to any comment. Clicking Reply should open an input only for that specific comment (others unaffected). Render comments hierarchically with indentation. Concepts: components, recursion, tree. Framework focus: Angular templates…

Use a standalone Angular root component.
Users can add top-level comments via a textarea + Add button.

What you’ll build / What this tests

This premium angular coding focuses on Nested Comments (Infinite Replies). You’ll apply components and recursion thinking with intermediate level constraints. The prompt emphasizes Build a nested comments panel that supports infinite-depth replies. Users can add top-level comments and reply….

Learning goals

Translate the prompt into a clear angular API signature and return shape.
Apply components, recursion, tree techniques to implement nested comments (infinite replies).
Handle intermediate edge cases without sacrificing readability.
Reason about time/space complexity and trade-offs in angular.

Key decisions to discuss

Define the exact input/output contract before coding.
Decide on concurrency and error propagation behavior.
Prioritize predictable edge-case handling over micro-optimizations.

Evaluation rubric

Correctness: covers required behaviors and edge cases.
Clarity: readable structure and predictable control flow.
Complexity: avoids unnecessary work for large inputs.
API discipline: no mutation of inputs; returns expected shape.
Testability: solution is easy to unit test.

Constraints / Requirements

Use a standalone Angular root component.
Users can add top-level comments via a textarea + Add button.
Each comment shows a Reply button.
Clicking Reply opens a reply input ONLY under that comment.
Users can submit a reply, which becomes a child comment under the parent.
Support infinite nesting depth (replies can be replied to).
Render nested replies with visible indentation.
Submitting a top-level comment adds it to the list.
Clicking Reply on one comment toggles only that comment’s reply input.
Submitting a reply appends a child comment under the correct parent.

Mini snippet (usage only)

// Example usage
const input = /* nested comments (infinite replies) input */;
const result = solve(input);
console.log(result);

// Edge case check
const empty = input ?? null;
const fallback = solve(input);
console.log(fallback);

// Expected: describe output shape, not the implementation
// (no solution code in preview)

Common pitfalls

Mutating inputs instead of returning a new value.
Skipping edge cases like empty input, duplicates, or nulls.
Overlooking time complexity for large inputs.