Learn how to select the right data structure based on the job: ordered lists, simple dictionaries, unique values or key-value pairs with flexible keys.
Think first about the dominant operation: list, lookup, deduplication or indexing.
There is no universally best structure. The right choice depends on how the data will be used during the life of the feature.
If you need ordered iteration, use `Array`. If you need uniqueness, use `Set`. If you need repeated lookups by key, `Map` is often clearer than scanning arrays again and again.
The right fit becomes clearer when you compare realistic usage.
`Array` is the default when order matters. `Object` is strong for modeling one named entity. `Set` removes duplicates and answers membership questions directly. `Map` makes repeated lookups by id or complex keys much easier to express.
The more often you do the same kind of operation, the more important the right structure becomes.
They remove extra logic when the requirements match their strengths.
A `Set` is excellent for selected ids, active permissions, deduplicated tags or values already seen during pagination. A `Map` is excellent for lookup tables, local caches and repeated access by id.
Once the structure matches the operations, the code becomes shorter and more honest about what the feature actually needs.