How do hash maps handle collisions, and why is average O(1) but worst O(n)?

Question

"Explain how JavaScript Map handles hash collisions internally."

Interview OS Community · Accepted Answer

## Collision Handling

**Chaining**: Colliding keys stored in linked list at same bucket.
**Open Addressing**: Try next bucket (linear probing).

```typescript
// Two keys hash to same index
bucket[42] → [{ key: "name", value: "Alice" }] → [{ key: "mane", value: "Bob" }]
```

| Case | When | Complexity |
|------|------|------------|
| Average | Good hash, low load | O(1) |
| Worst | All keys collide | O(n) |

V8 optimizations: Hidden classes (same object shape = fast), inline caching (remember property location).

Question Details