What are Map and Set?

In modern JavaScript, the Map and Set data structures are powerful built-in collections that significantly expand a developer's capabilities compared to traditional objects and arrays. These tools provide high performance and convenience when solving everyday programming tasks.

The Map collection represents a classic key-value pair dictionary. The main advantage of Map is that absolutely any data type can act as a key, including objects, functions, and primitive types, whereas in regular objects, keys can only be strings or symbols.

To create a new collection, the simple constructor syntax `new Map()` is used. After that, standard methods are used to populate and manage data: `set()` to add a pair, `get()` to retrieve a value by key, and the `has()` method, which allows you to quickly check for the existence of a key in the collection.

The Set collection, in turn, is a set of unique values of any type, where each element can occur only once. This makes Set an ideal tool for filtering duplicates from arrays or checking for the presence of elements in large data sets.

The main methods for working with a set include `add()` to add a new element, `has()` to check for its existence, and `delete()` to remove it. To convert a set back into an array, you can use the spread operator or the `Array.from()` method.

An important addition to standard collections is their "weak" counterparts — WeakMap and WeakSet. The main feature of WeakMap and WeakSet is that they use weak references to key-objects or elements, which allows the garbage collector to automatically remove them from memory.

The use of WeakMap and WeakSet prevents memory leaks in complex applications, as elements are automatically deleted as soon as other references to them disappear. This makes them indispensable for data caching and storing private object properties.