A Map stores values by key (key → value). Use it when you need fast lookup by an identifier (e.g., email → user) instead of by numeric index; a hash map is usually O(1) average for get/put.
Advanced answer
Deep dive
Expanding on the short answer — what usually matters in practice:
Context (tags): map, dictionary, hashmap, lookup
Complexity: compare typical operations (average vs worst-case).
Invariants: what must always hold for correctness.
When the choice is wrong: production symptoms (latency, GC, cache misses).
Explain the "why", not just the "what" (intuition + consequences).
Trade-offs: what you gain/lose (time, memory, complexity, risk).
Edge cases: empty inputs, large inputs, invalid inputs, concurrency.
Examples
A tiny example (an explanation template):
// Example: discuss trade-offs for "what-is-a-map-(dictionary)-and-when-would-you-us"
function explain() {
// Start from the core idea:
// A Map stores values by key (key → value). Use it when you need fast lookup by an identifie
}
Common pitfalls
Too generic: no concrete trade-offs or examples.
Mixing average-case and worst-case (e.g., complexity).