How does the garbage collector work in JavaScript?

In JavaScript, the garbage collector works automatically by identifying objects that are no longer accessible from reachable roots (such as the global object, current function call, etc.) and freeing the memory they occupy.

Main mechanisms:

• Reference Counting: An outdated method that counts the number of references to an object. Memory is freed when the count reaches zero. Disadvantage: cannot handle cyclic references.
• Mark and Sweep: A modern, most common method.
  1. Marking: Starting from the roots, the garbage collector recursively traverses the object graph, marking all accessible objects.
  2. Sweeping: It then traverses the heap and removes all objects that were not marked as accessible.

The advantage of "Mark and Sweep" over "Reference Counting" is that it correctly handles cyclic references.

JavaScript engines (for example, V8 in Chrome) constantly monitor memory usage and run the garbage collector as needed. Developers cannot directly control this process but can indirectly influence it by avoiding unnecessary references and managing the lifecycle of complex objects.