5.10 Garbage Collection
In low-level languages like C or C++, you have to allocate memory when you create an object and free it yourself when you are done. JavaScript works very differently. As soon as you initialise a new object, the engine automatically allocates memory for it. You use the object, and once you no longer need it, you do not have to free anything explicitly.
The JavaScript engine includes what we call a garbage collector. Its job is to find variables and constants that are no longer used anywhere in your program and to release the memory that had been allocated for them. Allocation and deallocation both happen behind the scenes, in the background.
What this means for you
- You have no direct control over the garbage collector — you cannot ask it to run, and you cannot tell it which variable to remove.
- It uses internal heuristics to decide when to run and what is no longer reachable.
- This frees you from manual memory management, but you still have to design your code so that references you no longer need are dropped (set to
null, leave their scope, etc.).
Based on its own (complex) algorithms, the garbage collector continuously detects which variables are no longer in use and automatically reclaims their memory. That is all there is to it for this short video on garbage collection in JavaScript — see you in the next one.
Summary
This lesson covers garbage collection in JavaScript, a mechanism that automatically manages memory allocation and deallocation. Unlike low-level languages such as C and C++ where developers must manually allocate and free memory, JavaScript handles this automatically through its garbage collector. The garbage collector runs continuously in the background using complex algorithms to identify variables and objects no longer in use, then frees their allocated memory without requiring any developer intervention or control.
Key points
- JavaScript features automatic garbage collection, eliminating the need for manual memory management required in languages like C and C++
- Memory is automatically allocated to objects when created and initialized in the program, and deallocation is handled seamlessly by the garbage collector
- The garbage collector operates in the background without developer visibility or control—you cannot manually trigger it or determine when variables are removed from memory
- Developers have no ability to control garbage collection behavior or timing due to the complex algorithms the garbage collector uses to identify unused variables
- The automatic memory management system prevents developers from needing to explicitly deallocate memory after using objects
FAQ
How does JavaScript's garbage collection differ from manual memory management in languages like C++?
In C++ and other low-level languages, developers must manually allocate and deallocate memory. JavaScript automates this process—memory is automatically allocated when objects are created and automatically freed when they're no longer used, eliminating the need for developers to manage memory manually.
Can I control when the garbage collector runs or which variables it removes?
No. The garbage collector operates completely in the background using complex algorithms. You have no control over its execution timing or which variables are targeted for memory deallocation.
What happens to memory allocated to variables I'm no longer using?
The garbage collector identifies these unused variables and objects, then automatically deallocates their memory so it can be reused by other processes in the JavaScript engine.