Global Variable in Javascript

In JavaScript, a global variable is a variable declared outside any function or block scope.

Global variables are accessible from any part of our code, including functions, making them visible and modifiable throughout the program.

However, it's important to use global variables judiciously, as they can lead to potential issues such as naming conflicts and unintended modifications.

Best Practices for Using Global Variables in Javascript:

Minimize Usage: Try to avoid using global variables and instead prefer passing data as arguments to functions or encapsulating data within modules.
Use Proper Naming: Keep global variables seperate from source code and use unique Naming conventional for Global Variables and give them descriptive names to reduce the risk of naming conflicts and improve code readability.
Consider Global Constants: If the Global variable value is Constant then consider declaring it as a global constant using the `const` keyword.
Use Strict Mode: Enabling strict mode ("use strict";) helps to catch common errors sooner and prevents accidental global variable creation.

Way of Declaring Global Variable:

// Declaring a global variable
var globalVariable = "Declared global variable";

function globalVariableExample() {
  // Accessing the global variable within a function
  console.log(globalVariable);
}

// Modifying the global variable
globalVariable = "Modified global variable";

// Calling the function to demonstrate access to the global variable
globalVariableExample();

It's worth noting that starting from ECMAScript 6 (ES6), we can also use the `let` and `const` keywords to declare global variables:

Example:

// Using let to declare a global variable
let globalVariableLet = "I am a global variable with let";

// Using const to declare a global variable
const globalVariableConst = "I am a global variable with const";

Note:

"var", "let", and "const" can be used for global variable declarations, the scoping rules differ, and it's generally recommended to use "let" and "const" over "var" for better control of the variable scope.

Potential Issues with Global Variables:

Namespace Pollution: Global variables are accessible in the code from anywhere, It can cause conflict with variables in other parts of the code, which leads to bugs and unexpected behaviour.
Accidental Reassignment: In larger codebases, it's easy to reassign global variables, leading to difficult-to-debug issues inadvertently.
Testing and Debugging: If our code relies heavily on global variables, testing and debugging will be more challenging, as it may have hidden dependencies and side effects.

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