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Object tree traversal

Q: Object tree traversal

**Target Audience:** Engineers preparing for practical JavaScript coding interviews. **Difficulty:** Easy > **How to read this doc:** the real, easy-to-miss edge case this question tests — that a real ARRAY value must be treated as a LEAF, not recursed into further, even though a JavaScript array is genuinely, technically an object too — was verified directly against a tree containing a real array value: it correctly appeared as a single leaf entry, not decomposed into per-index entries. ## 1. The problem, restated Recursively walk a nested plain-object tree, and for every genuine LEAF (a value that is NOT itself a plain object to recurse into — critically including a real ARRAY, which must be treated as a leaf despite technically being an object), collect that leaf's own value together with the FULL dot-notation path of keys leading to it from the root. ## 2. Clarifying questions a strong candidate asks | Question | Why it matters | | :--- | :--- | | Arrays: leaf or recurse? | Tr

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The problem

Problem, as an interviewer would state it: "Implement traverseTree(obj) — recursively walking a nested plain-object tree and collecting every LEAF value together with its own full dot-notation path."

Examples:

Code

traverseTree({a: 1, b: {c: 2}});
// [{path: "a", value: 1}, {path: "b.c", value: 2}]

Clarifying questions expected:

Should a real ARRAY value be treated as a leaf itself, or recursed into like a nested object — since arrays are genuinely objects too in JavaScript?
What real, correct format should the path take — a dot-separated string, or an array of keys?
Does the traversal need to visit keys in any particular real order (e.g. matching Object.keys's own order)?

Code / implementation expected: Yes — real, direct proof against a genuinely nested, multi-level tree, confirming correct leaf detection including the real array-as-leaf edge case.

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: the real, easy-to-miss edge case this question tests — that a real ARRAY value must be treated as a LEAF, not recursed into further, even though a JavaScript array is genuinely, technically an object too — was verified directly against a tree containing a real array value: it correctly appeared as a single leaf entry, not decomposed into per-index entries.

1. The problem, restated

Recursively walk a nested plain-object tree, and for every genuine LEAF (a value that is NOT itself a plain object to recurse into — critically including a real ARRAY, which must be treated as a leaf despite technically being an object), collect that leaf's own value together with the FULL dot-notation path of keys leading to it from the root.

2. Clarifying questions a

The solution is hidden so you can try first

7 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: traverseTree() collects every leaf's exact path and value from a real nested tree, correctly treating a real array value as a single leaf

Practice

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