What is the difference between Map and WeakMap?

Main differences between Map and WeakMap:

• Keys:

  • Map can use any values (primitives and objects) as keys.
  • WeakMap only accepts objects as keys.

• Garbage collection:

  • In Map, keys and values are held with strong references, so objects are not removed from memory as long as there is a reference in Map.
  • In WeakMap, keys are held with weak references, meaning if the object key is no longer used elsewhere, it can be garbage collected along with the associated value.

• Iteration:

  • Map supports iteration over its elements (methods like forEach, keys, values, etc.).
  • WeakMap does not support iteration because keys can disappear at any moment.

• Usage:

  • Map is suitable when you need to store key-value pairs with any key types and want to iterate over them.
  • WeakMap is useful for storing data related to objects without preventing their removal from memory (e.g., for private object data).

Example of using WeakMap to store private data:

const privateData = new WeakMap();

class User {
  constructor(name) {
    privateData.set(this, { name });
  }
  getName() {
    return privateData.get(this).name;
  }
}

Here, user data is not accessible from outside and is automatically removed when the User object is deleted.