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Custom Set class with hash

Q: Custom Set class with hash

**Target Audience:** Engineers preparing for practical JavaScript coding interviews. **Difficulty:** Medium > **How to read this doc:** the real, defining test of any hash table implementation — correctly handling a COLLISION, where two different values land in the same bucket — was verified directly with a real, deliberately forced single-bucket scenario (3 values, 1 bucket), confirming all 3 remained correctly, independently trackable. ## 1. The problem, restated A hash table maps each value to a bucket INDEX via a hash function, storing the value in that bucket. Since different values can genuinely hash to the SAME bucket (a collision), each bucket needs to hold a real LIST of values (not just one), with membership checks and deletions searching within that specific bucket's own list. ## 2. Clarifying questions a strong candidate asks | Question | Why it matters | | :--- | :--- | | Collision handling strategy? | "Separate chaining" (each bucket is its own array) is the real, st

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The problem

Problem, as an interviewer would state it: "Implement a Set-like class from scratch using an actual hash table — an array of 'buckets', each holding a list of values that hash to the same slot — supporting add, has, and delete."

Examples:

Code

const set = new HashSet();
set.add("apple").add("banana");
set.has("apple"); // true

Clarifying questions expected:

How should hash COLLISIONS (two different values landing in the same bucket) be handled?
Does adding an already-present value need to be a genuine no-op, matching real Set semantics?
Is a fixed bucket count acceptable, or should the table resize as it grows?

Code / implementation expected: Yes — real, direct proof of correct add/has/delete, PLUS a deliberately forced real collision scenario confirming multiple colliding values remain correctly, independently trackable.

js-coding
utility
algorithm

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Solution

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

How to read this doc: the real, defining test of any hash table implementation — correctly handling a COLLISION, where two different values land in the same bucket — was verified directly with a real, deliberately forced single-bucket scenario (3 values, 1 bucket), confirming all 3 remained correctly, independently trackable.

1. The problem, restated

A hash table maps each value to a bucket INDEX via a hash function, storing the value in that bucket. Since different values can genuinely hash to the SAME bucket (a collision), each bucket needs to hold a real LIST of values (not just one), with membership checks and deletions searching within that specific bucket's own list.

2. Clarifying questions a strong candidate asks

Question	Why it matters

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: a HashSet correctly handles normal usage AND a deliberately forced single-bucket collision, tracking every colliding value independently

Practice

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