Hash tables: fast lookups and collisions

From text to index

The hash function must be deterministic and distribute keys. Modulo fits the result into the bucket count.

function hash(key, size) {
  let total = 0;
  for (const char of key) total += char.charCodeAt(0);
  return total % size;
}

Two keys, one bucket

A collision is not an error; it is part of the design. Separate chaining stores a small collection per bucket; open addressing finds another position.

• More buckets reduce collisions and consume more memory.
• A poor function concentrates keys.
• Load factor tells you when to resize.

In products: use Map

Implementing a table teaches the concept. In JavaScript applications, Map already handles identity, growth, and collisions robustly.