![]() There's no way for us to access the two objects anymore. This happens when one or more objects reference each other, but they can't be accessed through code anymore.īecause son and dad objects reference each other, the algorithm won't release the allocated memory. The problem with this algorithm is that it doesn't consider cyclic references. Note how in the last frame only hobbies stays in the heap since it's the object one that has a reference in the end. Let's have a look at the following example. It collects the objects that have no references pointing to them. I'll discuss the most used ones in this section: The reference-counting garbage collection and the mark and sweep algorithm. Some algorithms offer a good approximation to the problem. The main issue with this is that whether or not some memory is still needed is an undecidable problem, which means that there can't be an algorithm that's able to collect all the memory that's not needed anymore in the exact moment it becomes obsolete. Once the JavaScript engine recognizes that a given variable or function is not needed anymore, it releases the memory it occupied. More specifically, the garbage collector takes care of this. Just like memory allocation, the JavaScript engine handles this step for us as well. We now know how JavaScript allocates memory for all kinds of objects, but if we remember the memory lifecycle, there's one last step missing: releasing memory. Going more into detail here would be out of the scope of this article, but if you want to learn more about it, let me know in the comments and subscribe to my newsletter. References are a core concept of how JavaScript works. This creates a new object in the heap and a reference to it in the stack. In the captions I mention what is being allocated: Let's have a look at a few code examples. To get an overview, here are the features of the two storages compared side by side: Stack Instead, more space will be allocated as needed.Īllocating memory this way is also called dynamic memory allocation. ![]() Unlike the stack, the engine doesn't allocate a fixed amount of memory for these objects. The heap is a different space for storing data where JavaScript stores objects and functions. The limits of these values and the entire stack vary depending on the browser. The process of allocating memory right before execution is known as static memory allocation.īecause the engine allocates a fixed amount of memory for these values, there is a limit to how large primitive values can be. Since the engine knows that the size won't change, it will allocate a fixed amount of memory for each value. In JavaScript, this includes primitive values ( strings, numbers, booleans, undefined, and null) and references, which point to objects and functions. Static data is data where the engine knows the size at compile time. You might know the stack from the first part of this series on the call stack and event loop, where I focused on how it's used to keep track of the functions that the JS interpreter needs to call.Īll the values get stored in the stack since they all contain primitive values.Ī stack is a data structure that JavaScript uses to store static data. Heaps and stacks are two data structures that the engine uses for different purposes. JavaScript engines have two places where they can store data: The memory heap and stack. The next question that came to my mind was: Where is this going to be stored? We now know that for everything we define in JavaScript, the engine allocates memory and frees it up once we don't need it anymore. " Objects" in the context of memory management doesn't only include JS objects but also functions and function scopes. Once the allocated memory is released, it can be used for a new purpose. ![]() This step is handled as well by the JavaScript engine. Using memory is something we do explicitly in our code: Reading and writing to memory is nothing else than reading or writing from or to a variable. JavaScript takes care of this for us: It allocates the memory that we will need for the object we created. In JavaScript, when we create variables, functions, or anything you can think of, the JS engine allocates memory for this and releases it once it's not needed anymore.Īllocating memory is the process of reserving space in memory, while releasing memory frees up space, ready to be used for another purpose.Įvery time we assign a variable or create a function, the memory for that always goes through the same following stages: ![]()
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