HashMap & HashSet (JavaScript)

A custom implementation of HashMap and HashSet data structures built from scratch in JavaScript.
This project focuses on understanding how hash-based data structures work internally, including hashing, load factors, dynamic resizing, and efficient data storage.

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Overview

The goal of this project is to recreate the core behavior of hash maps and hash sets without relying on JavaScript’s built-in Map or Set. Both implementations use a fixed-size bucket array, a custom hash function, and automatic resizing when a predefined load factor is exceeded.

Insertion order is not preserved, which is expected behavior for hash-based data structures.

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HashMap

The HashMap stores key–value pairs using string keys only.

Supported Methods

• set(key, value) — Adds a new key–value pair or updates an existing key
• get(key) — Returns the value associated with a key, or null if not found
• has(key) — Returns true if the key exists, otherwise false
• remove(key) — Removes a key and returns true if successful
• length() — Returns the number of stored entries
• clear() — Removes all entries
• keys() — Returns an array of all stored keys
• values() — Returns an array of all stored values
• entries() — Returns an array of [key, value] pairs

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HashSet

The HashSet stores unique string keys without associated values.
It follows the same hashing and resizing logic as the HashMap implementation.

Supported Methods

• set(key) — Adds a key if it does not already exist
• get(key) — Returns the key if found, otherwise null
• has(key) — Returns true if the key exists
• remove(key) — Removes a key and returns true if successful
• length() — Returns the number of stored keys
• clear() — Removes all keys
• keys() — Returns an array of stored keys

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Implementation Details

• Buckets are stored in a fixed-size array
• A prime-number-based hash function is used
• Modulo is applied during hashing to prevent integer overflow
• The load factor is set to 0.75
• When the load factor is exceeded, capacity is doubled and all entries are re-hashed
• Keys are limited to strings only