Describe Closure concept in JavaScript as best as you could

A closure in JavaScript is a powerful and fundamental concept that involves the behavior of functions and the variables defined in their scope. At its core, a closure is a function that retains access to its lexical scope, even when that function is executed outside of its original context.

Understanding Scope and Lexical Environment

To understand closures, it's essential to first grasp the concepts of scope and lexical environments. Scope in JavaScript determines the accessibility of variables and functions at various parts of the code. There are mainly two types of scope:

1. Global Scope: Variables defined outside any function or block. These variables are accessible from any part of the code.
2. Local Scope: Variables defined inside a function or a block. These are only accessible within the function or block they are defined in.

The lexical environment refers to the environment in which the function was declared, and this environment determines the variables that the function can access. Lexical scoping means that the accessibility of variables is determined by the position of the variables within the nested function scopes[1][2][3].

How Closures Work

A closure occurs when a function is defined inside another function, allowing the inner function to access the outer function's variables. This inner function will retain access to the outer function’s variables even after the outer function has finished execution. This behavior is what we call a closure[1][2][3][4].

Practical Example of Closure

Consider the following code snippet:

function outerFunction() {
    let outerVariable = 100;

    function innerFunction() {
        console.log(outerVariable);
    }

    return innerFunction;
}

let resultFunction = outerFunction();
resultFunction();  // Outputs: 100

In this example, innerFunction is a closure. It is defined within outerFunction and has access to outerVariable, a variable in the outer function's scope. Even after outerFunction has completed execution, and resultFunction is called outside of outerFunction, innerFunction still has access to outerVariable. This is possible because innerFunction closes over (or captures) the variable outerVariable.

Use Cases for Closures

Closures are useful in several practical s...