In JavaScript, both Map and Object can store key-value pairs, but they have different features, performance characteristics, and use cases. Here’s a detailed comparison:
| Aspect | Object | Map |
| Key Types | Keys must be strings or symbols (other types are coerced to strings). | Keys can be of any type, including objects, functions, and primitives. |
| Order of Keys | String keys are ordered in insertion order (since ES6), but numerical keys are sorted numerically. | Keys maintain the exact insertion order, regardless of their type. |
| Performance | Optimized for properties that are strings. | More efficient for frequent additions, deletions, and lookups of key-value pairs. |
| Default Properties | Inherits from Object.prototype, which may introduce unintended properties like toString. | Does not inherit from Object.prototype, so there are no default properties. |
| Size Property | No direct size property; must use Object.keys(obj).length to determine the number of keys. | Has a size property to directly get the number of entries. |
| Iteration | Requires manual iteration using Object.keys, Object.values, or Object.entries. | Provides built-in methods like map.keys(), map.values(), map.entries(), and forEach. |
| Serialization | Can be easily serialized and deserialized with JSON.stringify and JSON.parse. | Requires custom handling for serialization and deserialization. |
| Use Case | Suitable for simple key-value storage when keys are strings or when working with JSON. | Ideal for cases requiring complex keys or frequent additions and deletions of entries. |
Use Cases for Object
- When you need a simple structure for key-value pairs where keys are strings or symbols.
- When working with existing codebases or libraries that expect
Objectinstances. - When JSON serialization/deserialization is required.
Use Cases for Map
- When you need non-string keys, like objects or functions.
- When insertion order matters.
- When you need a cleaner API for working with key-value pairs, especially for larger datasets or frequent updates.