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In JavaScript, function scope defines the boundaries within which variables and functions are accessible. Variables declared inside a function are confined to that function and cannot be accessed outside of it. This is an essential concept to understand because it ensures proper encapsulation and avoids unintentional interference between different parts of the code.

1. Definition of Function Scope:
Function scope means variables and functions declared within a function are only accessible inside that function. This creates a self-contained block of code, protecting it from external manipulation.

2. Encapsulation and Isolation:
Variables within a function are isolated, preventing them from conflicting with variables in the global scope or in other functions. This ensures clean and modular code.

3. Access Rules:
Any variable declared using `var`, `let`, or `const` inside a function cannot be accessed outside of it. The function scope restricts their availability to the function body.

4. Nested Scopes:
Functions can be defined inside other functions. The inner function has access to variables in the outer function (lexical scoping), but the reverse is not true. This allows for flexible and controlled access to data.

5. Global Scope vs Function Scope:
Variables declared outside any function are in the global scope and are accessible everywhere in the program. Function-scoped variables, however, are not available globally and remain private to the function.

6. Benefits of Function Scope:
- Prevents Global Namespace Pollution: Keeps variables from accidentally affecting other parts of the program.
- Improves Code Readability and Debugging: Variables are logically grouped where they are needed.
- Promotes Reusability and Modularity: Functions can work independently without depending on external variables.

7. Practical Application:
Function scope is widely used in web development to manage data securely and efficiently, particularly in scenarios like closures, callbacks, and event listeners.

8. Common Misunderstandings:
Beginners often confuse function scope with block scope (specific to `let` and `const`) or assume global variables are always accessible. Clarifying these concepts helps in writing efficient and bug-free code.

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