Data structures: choosing where information lives

Ask the right question

Do not ask which structure is best. Ask which operation you need most often: index access, key lookup, tail insertion, or arrival order.

• Array: order and index access.
• Set: unique values.
• Map: key lookup.
• Stack: last in, first out.
• Queue: first in, first out.

A cart and an index

A cart can be an array because order matters. An id index can be a Map because finding without scanning matters.

const productsById = new Map(
  products.map((product) => [product.id, product])
);

productsById.get('prod-42');

Every choice has a cost

Two structures can speed up reads but must stay synchronized on writes. Measure the dominant operation before adding indexes.