JavaScript uses a garbage collection mechanism to manage memory automatically

JavaScript Garbage Collection

JavaScript uses a garbage collection mechanism to manage memory automatically. The primary garbage collection algorithm used by most JavaScript engines is called "mark-and-sweep." This process ensures that memory that is no longer reachable or in use is reclaimed and made available for future allocations.

How It Works

1. Allocation: When a variable is declared and initialized, memory is allocated for it. In the case of local variables, this happens when the function is called.

2. Reachability: The garbage collector periodically checks which variables are still reachable or accessible. A variable is considered reachable if it can be accessed directly or indirectly by the executing code.

3. Marking: During the "mark" phase, the garbage collector identifies all reachable objects by traversing the graph of references starting from the root (global objects and currently executing functions).

4. Sweeping: In the "sweep" phase, the garbage collector reclaims memory occupied by objects that were not marked as reachable, effectively deleting those objects and freeing up memory.

Local Variables

Local variables in a function are created and initialized when the function is called. These variables are placed on the call stack or in the function's execution context. Once the function execution is completed, the local variables go out of scope, meaning they are no longer accessible from the executing code.

Example

Here's an example to illustrate this:

function exampleFunction() {
    let localVar = 10; // This is a local variable
    console.log(localVar);
}

exampleFunction();
// After the function call, localVar goes out of scope
// Trying to access localVar here would result in a ReferenceError

In the example above, localVar is created when exampleFunction is called. After the function completes execution, localVar goes out of scope, and the memory allocated for it can be reclaimed by the garbage collector.

Block Scope with let and const

Variables declared with let and const are block-scoped. This means they are limited to the block in which they are defined and go out of scope once the block is exited.

function anotherFunction() {
    if (true) {
        let blockScopedVar = 'I am block scoped';
        const blockScopedConst = 'I am also block scoped';
        console.log(blockScopedVar);   // This works
        console.log(blockScopedConst); // This works
    }
    // blockScopedVar and blockScopedConst are not accessible here
    // Trying to access them here would result in a ReferenceError
}

anotherFunction();

In this example, blockScopedVar and blockScopedConst are created when the block (the if statement) is executed and are automatically cleaned up by the garbage collector once the block is exited.

Summary

JavaScript's garbage collector handles memory management by automatically freeing up memory for variables that go out of scope, including local variables declared within functions and blocks. This process helps prevent memory leaks and ensures efficient use of memory during program execution.