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Find a Node in a DOM Tree (DFS/BFS)

By FrontendAtlas Team · Updated Feb 1, 2026

Implement findNode(root, predicate) to traverse the DOM and return the first matching element. Use DFS/BFS with early exit. Complexity: O(n) time, O(h) recursion stack.

What you’ll build / What this tests

This premium javascript coding focuses on Find a Node in a DOM Tree (DFS/BFS). You’ll apply dom and tree thinking with intermediate level constraints. The prompt emphasizes Implement findNode(root, predicate) to traverse the DOM and return the first matching element. Use DFS/BFS with….

Learning goals

Translate the prompt into a clear javascript API signature and return shape.
Apply dom, tree, traversal techniques to implement find a node in a dom tree (dfs/bfs).
Handle intermediate edge cases without sacrificing readability.
Reason about time/space complexity and trade-offs in javascript.

Key decisions to discuss

Define the exact input/output contract before coding.
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

Avoid deep recursion issues on large inputs.
Do not access the real DOM; use the provided node shape.
Handle empty or missing inputs without throwing errors.
Keep runtime close to linear time where possible.
Prefer a pure function: no side effects beyond the return value.

Mini snippet (usage only)

// Example usage
const root = /* find a node in a dom tree (dfs/bfs) input */;
const predicate = /* config */;
const result = findNode(root, predicate);
console.log(result);

// Edge case check
const empty = root && predicate ?? null;
const fallback = findNode(root, predicate);
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.