I could store key-value pairs in a simple Object. I can retrieve those values, delete keys, and detect whether something is stored at a key. So why the hell should I use a Map instead of an Object???
Discover the power of Maps: less hairy bugs, better developer experience, better performance.
Anything can be used as a key for a Map
While the keys of an Object must be Strings, any value can be used as key in a Map : a number will remain a number, and you can even use an Object as a key!
On the other hand, Objects automatically convert non-string keys into strings. If you try to use an object as a key, it might seem to work, but in reality, you will store {[object Object]: "your value"}, with object Object as a key! The next time you set a key with another object, you will simply overwrite your previous value. Good luck debugging those issues!
Maps are not polluted with built-in keys
Another source of fun bugs is that Object has a prototype. This means it has many default keys: valueOf, toString, toLocaleString, etc. Nothing prevents you from writing myObject["valueOf"] = "some stuff you want to store". I’ll let you imagine the surprises that could result from that.
You can prevent this behavior by creating an object with Object.create(null) but who actually does that?
Maps don’t have this issue. Maps are “clean” at creation time.
Maps are more comfortable to use than Objects
Built-in functions make the iteration more natural
In terms of programming comfort, .keys(), .values(), .entries() feel more natural than Object.keys(myObject) or Object.entries(myObject).
Maps keep the insertion order
Unlike Objects, Maps preserve insertion order and ensure consistent performance across all browsers. You can iterate through the elements with a for (const [key, value] of myMap) loop, which returns an array of [key, value] pairs. This is still simpler than for (const [key, value] of Object.entries(myObject)).
It’s easy to get the size of a Map
Just write myMap.size!
For an Object, you need Object.keys(myObj).length.
Maps have better performance
Maps are optimized for key-value storage, making them faster than Objects for frequent insertions, deletions, or lookups. If you need to add and remove keys frequently, use Maps.
When should I keep using an Object?
Use an Object when you need a plain data structure with a well-defined set of keys. For example, if you have many Events that all have a title and date property, Objects are optimized for fast reads and writes. Objects are also better suited for JSON serialization.
