Lecture 184:- Revisiting Old Concepts - Scopes

In JavaScript, scope refers to the visibility or accessibility of variables, functions, and objects. The scope of a variable defines the portion of the program where the variable is accessible. In other words, it determines where in a program a variable can be accessed and manipulated.

There are two types of scope in JavaScript: global scope and local scope.

Global scope refers to the visibility of a variable or function throughout the entire JavaScript program. A variable or function declared outside of any function or block of code has global scope, meaning it can be accessed from anywhere in the program.

Local scope, on the other hand, refers to the visibility of a variable or function within a specific function or block of code. A variable or function declared within a function or block of code has local scope, meaning it can only be accessed within that specific function or block of code.

In JavaScript, variables declared with the var keyword have function scope, which means they are accessible within the function in which they are declared. However, variables declared with the let and const keywords have block scope, which means they are only accessible within the block of code in which they are declared (e.g. within a for loop or an if statement).

It's important to understand the concept of scope in JavaScript because it helps prevent naming collisions and can make your code more organized and efficient. Additionally, scoping rules can have an impact on the performance of your code, as variables declared in a narrow scope can be garbage collected sooner than variables declared in a broader scope.