Scope:
- The context in which a variable is accessible. Variables can have global scope or local scope based on where they are declared.
Global Scope:
- Variables declared outside any function or block, accessible from anywhere in the code.
Local Scope:
- Variables declared within a function or block, accessible only within that specific context.
Hoisting:
- JavaScript's default behavior of moving variable and function declarations to the top of their containing scope during the compile phase.
Temporal Dead Zone (TDZ):
- The period between the start of a block and the point where a let or const variable is declared, during which the variable cannot be accessed.
var Keyword:
- Declares a function-scoped or globally-scoped variable, which is hoisted and initialized with undefined.
let and const Keywords:
- Declare block-scoped variables, with const used for variables that should not be reassigned. They are hoisted but not initialized, preventing access before declaration.
Best Practices:
- Use let and const over var to leverage block scoping and avoid hoisting-related bugs.
- Limit the use of global variables to prevent naming conflicts and unintended interactions.

Early JavaScript (1995): Introduced the var keyword for variable declarations, which provided function scoping. This led to challenges in managing variable scope, especially in larger codebases.
Introduction of ES6 (2015): ES6 introduced let and const for block-scoped variable declarations, addressing many of the scoping issues associated with var. This enhancement promoted better code organization and reduced the likelihood of scope-related bugs.
Modern JavaScript Practices: Emphasize the use of let and const to define variables within appropriate scopes, enhancing code readability and maintainability. Understanding hoisting and the Temporal Dead Zone (TDZ) has become essential for writing robust JavaScript applications.

Avoiding Global Namespace Pollution:
- Excessive use of global variables can lead to conflicts and bugs in larger applications. Encapsulating variables within functions or blocks helps maintain a clean global namespace.
Hoisting Mysteries:
- Hoisting can lead to unexpected behaviors, such as variables being accessible before their actual declaration, which has puzzled many JavaScript developers.
const for Immutable Bindings:
- While const prevents reassignment of variables, it does not make objects or arrays immutable. Properties of const objects can still be modified.
Best Practices Influence:
- The introduction of let and const has influenced modern JavaScript coding standards, encouraging developers to write more predictable and maintainable code.
Function Scope vs. Block Scope:
- Prior to ES6, JavaScript only supported function scope (var). The introduction of block scope with let and const allowed for more granular control over variable accessibility.

Day 14: Understanding Scope: Global and Local Variables