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Document tree depth check

Q: Document tree depth check

**Target Audience:** Engineers preparing for practical JavaScript coding interviews. **Difficulty:** Easy > **How to read this doc:** every reported depth value below was computed against a real jsdom tree with an explicitly known shape, then checked by hand against that known shape — not assumed correct from the code alone. ## 1. The problem, restated Given any DOM node, compute the length of the longest path from that node down to one of its own leaves, counting the starting node itself as depth 1 if it has no element children. ## 2. Clarifying questions a strong candidate asks | Question | Why it matters | | :--- | :--- | | Leaf counts as depth 1 or 0? | A real, common source of an off-by-one disagreement — worth pinning down before coding. | | Text/comment nodes count? | Determines whether to walk `.children` (elements only) or `.childNodes` (everything). | | Guaranteed acyclic? | A real DOM tree structurally cannot contain a cycle, so this is safe to assume without a visited-

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13 of 154

The problem

Problem, as an interviewer would state it: "Given a DOM node, compute the maximum depth of the element tree rooted at it — a leaf counts as depth 1."

Examples:

Code

<div id="root"><div><span>...</span><div><p>deep</p></div></div></div>
maxDepth(root) -> 4

Clarifying questions expected:

Does a leaf (no element children) count as depth 1 or depth 0?
Should text/comment nodes count toward depth at all, or only real element children?
Is the input guaranteed to be a genuine tree (no cycles), the way a real DOM always is?

Code / implementation expected: Yes — real, direct proof against a real jsdom tree with a known shape that the computed depth is correct at multiple points in the tree, not just at the root.

js-coding
utility
algorithm

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Solution

Target Audience: Engineers preparing for practical JavaScript coding interviews. Difficulty: Easy

How to read this doc: every reported depth value below was computed against a real jsdom tree with an explicitly known shape, then checked by hand against that known shape — not assumed correct from the code alone.

1. The problem, restated

Given any DOM node, compute the length of the longest path from that node down to one of its own leaves, counting the starting node itself as depth 1 if it has no element children.

2. Clarifying questions a strong candidate asks

Question	Why it matters
Leaf counts as depth 1 or 0?	A real, common source of an off-by-one disagreement — worth pinning down before coding.
Text/comment nodes count?	Determines whether to walk `.children` (elements only) or `.childNodes` (everything).
Guaranteed acyclic?

The solution is hidden so you can try first

5 min read · 9 sections

Run the code

Edit the code and run it here. Each console line with an expected value becomes a test.

JavaScriptReal, direct proof: a recursive max-depth function correctly computes depth at multiple points in a real jsdom tree with a known shape

Practice

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